=Paper= {{Paper |id=Vol-3159/T3-2 |storemode=property |title=CoMaTa OLI- Code-Mixed Malayalam and Tamil Offensive Language Identification |pdfUrl=https://ceur-ws.org/Vol-3159/T3-2.pdf |volume=Vol-3159 |authors=F. Balouchzahi,S. Bashang,G. Sidorov,H. L. Shashirekha |dblpUrl=https://dblp.org/rec/conf/fire/BalouchzahiBSS21 }} ==CoMaTa OLI- Code-Mixed Malayalam and Tamil Offensive Language Identification== https://ceur-ws.org/Vol-3159/T3-2.pdf
CoMaTa OLI-Code-mixed Malayalam and Tamil
Offensive Language Identification
F. Balouchzahi1 , S. Bashang2 , G. Sidorov1 and H. L. Shashirekha3
1
  Instituto Politécnico Nacional (IPN), Centro de Investigación en Computación (CIC), Mexico City, Mexico
2
  Canara Bank School of Management Studies, Bangalore University, India
3
  Department of Computer Science, Mangalore University, Mangalore, India


                                         Abstract
                                         Offensive Language Identification (OLI) in code-mixed under-resourced Dravidian languages is a chal-
                                         lenging task due to the complex characteristics of code-mixed text and scarcity of digital resources and
                                         tools to process these languages. This paper describes the strategy proposed by our team MUCIC for the
                                         ’Dravidian-CodeMix-HASOC2021’ shared task which includes two tasks: Task 1 and Task 2, with the
                                         aim of classifying a given social media post/comment into one of two predefined categories: Offensive
                                         (OFF) and Not-Offensive (NOT) in both the tasks. While Task 1 aims at identifying Hate Speech (HS)
                                         contents in Tamil language in native script, Task 2 focuses on identifying HS contents in Tamil-English
                                         (Ta-En) and Malayalam-English (Ma-En) code-mixed texts in Roman script. Training the Machine Learn-
                                         ing (ML) classifiers using the most frequent char and word n-grams, the proposed methodology secured
                                         2nd , 1st , and 2nd ranks for Tamil, and Ta-En and Ma-En code-mixed texts with average weighted F1-scores
                                         of 0.852, 0.678, and 0.762 respectively.

                                         Keywords
                                         Code-mixed, HASOC, Dravidian languages, n-grams, Machine Learning




1. Introduction
The current era is witnessing a tremendous increase in the use of social media platforms all
over the globe. Covid-19 situation has increased this further since a year due to lockdown and
isolations [1]. Due to quick and easy access, people use social media as a mode of communication
to interact, connect, and express their thoughts and opinions about various things like a movie,
situation like Covid-19, the present situation in Afghanistan, and so on. It is observed that, in
multilingual societies like India, users may post their comments mixing two or more languages
in a sentence, word or sub-word which leads to generating a large amount of code-mixed
content [2, 3].
   Code-mixing plays a vital role in maximizing the communication effectively between social
media users. According to Pfaff et al. [4], the bilingual competence of individuals results in
producing more code-mixed content on social media. Code-mixing can also be considered as an

FIRE 2021, Forum for Information Retrieval Evaluation, December 13-17, 2021, India
" frs_b@yahoo.com (F. Balouchzahi); Sepidehbashang92@gmail.com (S. Bashang); sidorov@cic.ipn.mx
(G. Sidorov); hlsrekha@gmail.com (H. L. Shashirekha)
~ https://mangaloreuniversity.ac.in/dr-h-l-shashirekha (H. L. Shashirekha)
 0000-0003-1937-3475 (F. Balouchzahi)
                                       © 2021 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
    CEUR
    Workshop
    Proceedings
                  http://ceur-ws.org
                  ISSN 1613-0073       CEUR Workshop Proceedings (CEUR-WS.org)
asset that helps the bilingual/native speakers to convey certain meanings, special attitudes, or
emotions effectively, especially in a multilingual scenario where there are no equivalent lexical
items and cannot be translated into a second language.
   Some reasons for code-mixing in the Indian context are as follows:

    • Restricted vocabulary of individuals;
    • Habitual expression;
    • To convey special attitude or special meaning;
    • Mood of the speaker;
    • Identity marker;
    • Profession;
    • To show respect and relation;
    • To criticize.

   Models developed to process and analyse any monolingual data in general, may not give
good performance on code-mixed data due to the complexity and lack of standardization of
code-mixed data. Hence, research on code-mixed data of different levels of complexity should be
encouraged significantly for different applications like Sentiments Analysis (SA), HS detection,
and Offensive Language Identification (OLI). This, in turn, will contribute towards developing
better models and approaches to solve complex problems involving code-mixed data.
   The offensive content is a common impolite phenomenon in real life and has negative impacts
on individuals and societies. In fact, a person or a group of people can be targeted with offensive
language due to the same ethnicity, gender or sexual orientation, political affiliation, religious
belief, or any other characteristics [5]. Among the code-mixed content on social media, offensive
content targeting an individual or a group is increasing day-by-day. OLI task demands automated
methods as filtering such content manually is labor intensive and error prone.
   Kannada, Malayalam, and Tamil are the Dravidian languages spoken in Karnataka, Kerala
and Tamil Nadu states of India respectively. Despite their popularity these languages are under-
resourced due to the scarcity of digital resources and tools for processing these languages [6].
Further, the amount of work done on the Natural Language Processing (NLP) tasks of these
languages is very much limited [7, 8]. Usually, the native speakers of these Dravidian languages
mix English with their languages at different linguistic units such as sentence, word, morpheme
and sub-word to post comments and share information on social media which leads to the
generation of code-mixed data. The nature of code-mixed data and the under-resourcefulness
of Dravidian languages makes the OLI task more complex and challenging [9].
   OLI in Dravidian languages1 [10] is one of the shared tasks in FIRE 20212 which consists of
two tasks, Task 1 and Task 2, with the aim of classifying a comment/post into Offensive (OFF)
or NOT-Offensive (NOT) categories. Task 1 includes classifying comments written in Tamil
language in native script and contains an extra category for text written in other languages
that should be classified into not-Tamil, whereas Task 2 includes classifying comments in Ta-En
and Ma-En code-mixed texts written in Roman script.
   1
       https://competitions.codalab.org/competitions/31146
   2
       http://fire.irsi.res.in/fire/2021/home
   The literature and the findings of OLI shared task in DravidianLangTech-2021 [7] - the first
workshop on Speech and Language Technologies for Dravidian Languages3 , reveals that most
of the successful models in the shared task employed multilingual transformers. However, few
traditional Machine Learning (ML) models submitted to this task also performed well but used a
combination of complicated features extracted from texts instead of using any feature selection/
reduction algorithms. Using ML models with feature selection algorithms keeps the model
simple compared to using a transformer like BERT which is resource intensive.
   With the aim of exploring the neglected ML models, in this paper, we, team MUCIC, describe
the models submitted to the OLI shared task in FIRE 2021. In this proposed work, we extend our
previous work [9] by combining the most frequent word and char n-grams features extracted
from the text and used them to train the three individual ML classifiers as well as an ensemble
of these three ML classifiers. The results illustrate that the ML classifiers outperformed most of
the models submitted to the OLI shared task and obtained 2nd rank in Task 1 and 1st and 2nd
ranks in Task 2 for code-mixed Ta-En and Ma-En language pairs respectively. Further, team
MUCIC emerged as the best performing team in the shared task w.r.t the average of the scores
of the two tasks. The code for the proposed method is publicly available in our GitHub link4 .
   The rest of the paper is organized as follows: Section 2 describes the related work followed
by the proposed methodology in Section 3. Experiments and results are described in Section 4
and the paper concludes in Section 5.


2. Related Work
Research related to OLI in code-mixed texts is gaining lot of importance. Developing annotated
datasets is an initial and major step in promoting various NLP applications for any natural or
code-mixed language text. In this direction, Ta-En [11], Ka-En [12], and Ma-En[13] code-mixed
datasets have been developed for SA/OLI tasks. These datasets were provided to the participants
of the concerned shared tasks to develop and submit the working models for final evaluation
and ranking.
   OLI shared task in DravidianLangTech-2021 is the first workshop on Speech and Language
Technologies for Dravidian languages [7, 8]. Several models were submitted by the researchers
to this shared task and the top performing models are described below:
   Inspired by the work of Zampieri et al. [14], Chakravarthi et al. [7] organized a shared task
on OLI in code-mixed Dravidian languages, namely: Tamil, Malayalam and Kannada at various
degrees of complexity. Datasets for this work were collected from different YouTube comments
posted on movie trailers of Tamil, Kannada, and Malayalam in 2019. The authors adopted the
Comment Scraper tool5 as well as Langdetect6 library to distinguish the languages used in the
comments. Collected comments were classified into one of the six categories:
   1. Not Offensive (comment does not mean to offend a person or group)
   2. Offensive Untargeted (comment contains offensive words, but not directed at anyone)
   3
     https://dravidianlangtech.github.io/2021/
   4
     https://github.com/fazlfrs/CoMaTa-OLI
   5
     https://github.com/philbot9/youtube-remarkscraper
   6
     https://pypi.org/venture/langdetect/
   3. Offensive Targeted Individual (comment targets a person by offensive words)
   4. Offensive Targeted Group (comment contain offensive words targeting a group)
   5. Offensive Targeted Other (comment contains offensive words but the targeted entity is
      not clear)
   6. Not in intended language (comment written in languages other than the intended lan-
      guage)
In addition to the categories defined by Zampieri et al. [14], a new category “Not in intended
language” was added to incorporate remarks written in languages other than the intended
language. For instance, in the code-mixed Malayalam dataset, if the comment does not include
Malayalam words written either in Malayalam or Roman script, it is considered as ‘Not in
intended language’. Participating teams were ranked based on the average weighted F1-scores
of the predictions on the Test set.
   Multilingual transformers such as Multilingual BERT7 (mBERT), XLM-Roberta8 , and In-
dicBERT9 were widely used in the models submitted by the participants of the shared task and
some of the best performing models are briefly described below:
   Saha et al. [15] fine-tuned various multilingual transformers including XLM-Roberta, mBERT,
IndicBERT, and MuRIL10 individually using unweighted and weighted cross-entropy loss func-
tions for the shared task. For training, they used HuggingFace11 with PyTorch12 and the Adam
adaptive optimizer with an initial learning rate of 1e-5. They also proposed a new BERT-
Convolutional Neural Network (CNN) fusion classifier where they trained a single classifier on
the concatenated embeddings from BERT and CNN models. For the CNN model, they used the
128-dim final layer embeddings trained on Skipgram word vectors and for the fusion classifier,
a feed-forward neural network having four layers with batch normalization and dropout on the
final layer was used. Further, they used Genetic Algorithm (GA)-optimized weighted ensembling
and obtained average weighted F1-scores of 0.78 (1st rank) for Ta-En, 0.74 (2nd rank) for Ka-En,
and 0.97 (1st rank) for Ma-En language pairs.
   Jayanthi et al. [16] ensembled mBERT and XLM-Roberta models which were pre-trained
with their respective corpora utilizing Masked Language Modeling (MLM) objective. They
transliterated the given datasets and used the HuggingFace library for the implementation of
their backbone models. Further, they also proposed a fusion-architecture to leverage character-
level, subword-level, and word-level embedding to boost the performance of their models. Their
ensembled model secured the 1st rank for Ka-En, 2nd fpr Ma-En, and 3rd for Ta-En languages
pairs with 0.75, 0.97, and 0.76 average weighted F1-scores respectively.
   Vasantharajan et al. [17] fine-tuned the mBERT transformer for the task of OLI in Dravidian
languages. Primarily, in data pre-processing step, Emojis were converted into English text
using a dictionary of Emojis and punctuation were removed from the texts. They employed
BERT Tokenizer which converts the word into tokens and generates token ids, input masks (to
increase the performance), and input type ids according to the input word. In addition, they also
   7
      https://github.com/google-research/bert/blob/master/multilingual.md
   8
      https://huggingface.co/transformers/model_doc/xlmroberta.html
    9
      https://huggingface.co/ai4bharat/indic-bert
   10
      https://huggingface.co/google/muril-base-cased
   11
      https://huggingface.co/
   12
      https://pytorch.org/
added a dropout and pooled output layer and obtained 2nd , 5th , and 6th ranks for Ma-En, Ka-En,
and Ta-En language pairs with 0.96, 0.70, and 0.73 average weighted F1-scores respectively.
   In their proposed model, Li et al. [18] removed Emojis and extra blanks in the code-mixed
data to enhance the performance of the model and used class combination, class weights, and
focal loss to allay the class-imbalance issue that existed in the training data. Finally, employing
adversarial training to fine-tune XLM-Roberta and mBERT models, they achieved average
weighted F1- scores of 0.75, 0.94, and 0.72 with ensembling the fine-tuned models for Ta-En,
Ma-En, and Ka-En language pairs respectively.
   Along with transformers-based models, few ML-based models using n-grams of various levels
also performed well in the shared task. Few top performing ML based models are described
below:
   Balouchzahi et al. [9] proposed two models, namely, COOLI- Ensemble and COOLI-Keras.
COOLI-Ensemble is a Voting Classifier (VC) with three ML estimators, namely: Multi-Layer
Perceptron (MLP), eXtreme Gradient Boosting (XGB), and Logistic Regression (LR) and COOLI-
Keras is based on Deep Learning (DL) approach. Pre-processing includes de-emojizing (con-
verting Emoji to English text), removing punctuation, unnecessary characters and words of
length less than 2, and converting English words to lower case. A set of char sequences and
words are extracted as features and transformed to TFIDF vectors to train the learning models.
COOLI-Ensemble model outperformed the COOLI-Keras model for both Ma-En and Ta-En
language pairs and achieved 1st rank for Ma-En language pair with 0.97 average weighted
F1-score and 4th and 6th ranks with 0.75 and 0.69 average weighted F1-scores for Ta-En and
Kn-En language pairs respectively.
   Bharathi et al. [19] vectorized word n-grams using CountVectorizer and TfidfVectorizer and
concatenated them with mBERT embeddings vectors to train different ML classifiers, namely:
MLP, k-Nearest Neighbor (kNN), Support Vector Machine (SVM), Random Forest (RF), and
Decision Tree (DT) using these vectors. The best performances reported by the authors are the
average weighted F1-scores of 0.73, 0.95, and 0.70 for Ta-En, Ma-En, and Kn-En language pairs
respectively. Bhargav et al. [20] fed character n-grams vectors obtained by TfidfVectorizer for
Ta-En and Ka-En language pairs to LR classifiers and obtained vectors from MuRIL language
model for Ma-En texts to train a RF classifier. They obtained average weighted F1-scores of 0.95,
0.71, and 0.65 for Ma-En, Ta-En, and Ka-En language pairs respectively.
   Despite the several learning models and several features, none of the models promise 100%
accurate results which gives scope to explore further.


3. Methodology
The proposed strategy contains two main modules, namely: feature engineering and model
construction, which are detailed below:

    • Feature Engineering: This module consists of pre-processing texts by converting
      Emoji’s to English words followed by removing punctuation, unnecessary characters and
      words of length less than 2 and lower casing the English text. TfidfVectorizer from Sklearn
      library is used to extract word n-grams in the range (1, 3) and char n-grams in the range
      (2, 5) from the pre-processed text, limiting the features to 40,000 frequent features in each
Table 1
Total number of features
                                                Total number of n-grams
                   Tasks     Language
                                           Char n-grams in Word n-grams in
                                           the range (1, 3)  the range (2, 5)
                   Task 1       Tamil          159,597            104,816
                                Ta-En           99,110            107,951
                   Task 2
                                Ma-En          103,354            83,136




Figure 1: Feature engineering


      case. These 40,000 frequent features of each type are stacked to obtain 80,000 features’
      feature vector. The total number of features without any limitation are presented in Table
      1. Employing only the top frequent features reduces the dimensions and hence reduces
      the time taken to train the classifiers. In addition, it is expected that training the classifiers
      with only frequent features avoids overfitting and leads to enhancing the performance of
      classifiers. Figure 1 presents the graphical representation of feature engineering module.
    • Model Construction: The three ML classifiers, namely: Linear SVM (LSVM), LR, and
      Random Forest (RF), and their ensemble with soft voting as shown in Figure 2 are trained
      using the feature vectors obtained for the training set. In soft voting ensemble model, the
      prediction of estimators which are the probability values for classes will be weighted by
      the classifier’s importance and the largest sum of the weighted probabilities determine
      the final tag. The models are evaluated locally using the feature vectors obtained for the
      Development set and the predictions on the Test set are submitted to the organizers for
      final evaluation and ranking.

   Evidently, it is expected that finding the best range of char and word n-grams and selecting
a good number of features would improve the performances of the model. However, the idea
behind selecting only 40,000 top frequent features for each n-gram type in all language pairs
and choosing the widely used ML classifiers is to keep the proposed method simple but robust.
Figure 2: Voting classifier


Table 2
Statistics of Datasets
                  Tasks       Language    Labels     Train set   Dev set   Test set
                                           OFF         1,153                 118
                Task 1         Tamil       NOT         4,724       —         536
                                         Not-Tamil       3                    0
                                           OFF         1,980       475       395
                               Ta-En
                                           NOT         2,019       465       605
                Task 2
                                           OFF         1,952       478       325
                               Ma-En
                                           NOT         2,047       473       675


4. Experiments and Results
Datasets provided by the HASOC-DravidianCodeMix shared task [21, 22] organizers are col-
lected from social media. They contain Train, Development (Dev) and Test sets which includes
Tamil text in Tamil script for Task 1 and code-mixed texts in Ta-En and Ma-En language pairs
for Task 2. The statistics of the datasets given in Table 2 illustrate that the dataset is highly
imbalanced which make it more challenging.
   The performances of the models are evaluated and ranked by the organizers based on the
average weighted F1-scores. Table 3 presents the performances of ML classifiers on Development
set computed using Sklearn library for Task 2 only as Development set is not provided for Tamil
language in native script for Task 1. The results illustrate that the individual classifiers and
their ensemble obtained very competitive performances for both the language pairs. However,
for the Development set, LR and RF classifiers outperformed the other classifiers for both the
language pairs.
   Results obtained on Test sets show that LR classifier outperformed other classifiers for Tamil
and Ta-En language pair with average weighted F1-scores of 0.582 and 0.678 respectively.
However, RF classifier obtained highest results for Ma-En language pair with average weighted
F1-score of 0.762. The detailed performances of ML classifiers evaluated on Test sets are given
in Table 4.
Table 3
Results of Task 2 for the Development set
                     Language     Classifier    Precision    Recall   F1-score
                                     LR           0.881      0.881     0.881
                                    LSVM          0.865       0.865     0.865
                       Ta-En
                                     RF           0.864       0.860     0.859
                                  Ensemble        0.877       0.877     0.877
                                     LR           0.756       0.755     0.755
                                    LSVM          0.751       0.748     0.747
                      Ma-En
                                     RF           0.795      0.784     0.783
                                  Ensemble        0.785       0.780     0.780

Table 4
Results of Task 1 and Task 2 for the Test set
             Task Language Classifier           Precision   Recall    F1-score    Rank
                                       LR         0.850     0.861      0.852       2
                                      LSVM        0.839      0.852      0.843       -
               1       Tamil
                                       RF         0.830      0.846      0.811       -
                                    Ensemble      0.847      0.861      0.842       -
                                       LR         0.679     0.685      0.678       1
                                      LSVM        0.665      0.672      0.666       -
                       Ta-En
                                       RF         0.618      0.604      0.608       -
                                    Ensemble      0.677      0.681      0.678       -
               2
                                       LR         0.759      0.737      0.743       -
                                      LSVM        0.754      0.724      0.731       -
                       Ma-En
                                       RF         0.764     0.760      0.762       2
                                    Ensemble      0.768      0.749      0.754       -


   The confusion matrices for the best performing classifiers for each task are shown in Figure
3. LR classifiers have performed well for Task 1 and code-mixed Ta-En language pair of Task 2
and RF classifier has performed well for Ma-En language pair of Task 2 and the corresponding
confusion matrices are shown in Figure 3a, 3b and 3c respectively. Analysis of the confusion
matrices illustrate that classifiers were more successful in identifying NOT (not offensive) posts
due to the higher number of samples in this category in the given datasets for both the tasks.
   The comparison of the proposed strategy with the best performing teams of the shared task
in terms of average weighted F1-score is presented in Figure 4. It can be observed that, on
the average, team MUCIC outperformed all the other teams by obtaining average weighted
F1-scores of 0.852, 0.678, and 0.762 and securing 2nd , 1st , and 2nd ranks for Tamil (Task 1), Ta-En
and Ma-En language pairs (Task 2) respectively.


5. Conclusion and Future Work
This paper describes the strategy proposed by the team MUCIC for the Dravidian-CodeMix-
HASOC2021 shared task. In the proposed strategy, the top frequent char and word n-grams
selected from the texts are stacked and converted to TFIDF vectors for training the ML classifiers.
Figure 3: Confusion matrix of the best performing classifiers




Figure 4: Comparison of F1-scores of the best performing teams


Team MUCIC participated in both Task 1 and Task 2 and secured 2nd , 1st , and 2nd ranks for
Tamil and code-mixed Ta-En and Ma-En language pairs respectively. The proposed strategy out-
performed most of the models submitted by the participants to the shared task and became one
among the best performing teams. This work also proved the effectiveness of feature reduction
(even a simple algorithm) algorithms for classification tasks. The statistical feature selection
algorithms along with various feature sets to improve the performances of ML classifiers will
be explored further.
Acknowledgments
Team MUCIC sincerely appreciate the organizers for their efforts to conduct this shared task.


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