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The dataset generation failed because of a cast error
Error code: DatasetGenerationCastError
Exception: DatasetGenerationCastError
Message: An error occurred while generating the dataset
All the data files must have the same columns, but at some point there are 7 new columns ({'seats_won', 'election_type', 'notes', 'alliance', 'party', 'year', 'seats_contested'}) and 16 missing columns ({'admk_seats', 'inc_seats', 'iuml_seats', 'total_ac', 'cpim_seats', 'cpi_seats', 'dmdk_seats', 'source', 'vck_seats', 'district', 'dmk_seats', 'pmk_seats', 'ammk_seats', 'other_seats', 'bjp_seats', 'tvk_seats'}).
This happened while the csv dataset builder was generating data using
hf://datasets/ThinkPolitically/tamil-nadu-election-data/tn_election_party_results_2011_2026.csv (at revision 34bf6d8222cb5b4117d4f7994774567a82e8254b), ['hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_district_vote_share_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_election_party_results_2011_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_swing_constituencies_2011_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_tvk_booth_organisation_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_youth_turnout_2026.csv']
Please either edit the data files to have matching columns, or separate them into different configurations (see docs at https://hf.co/docs/hub/datasets-manual-configuration#multiple-configurations)
Traceback: Traceback (most recent call last):
File "/usr/local/lib/python3.14/site-packages/datasets/builder.py", line 1837, in _prepare_split_single
writer.write_table(table)
~~~~~~~~~~~~~~~~~~^^^^^^^
File "/usr/local/lib/python3.14/site-packages/datasets/arrow_writer.py", line 765, in write_table
self._write_table(pa_table, writer_batch_size=writer_batch_size)
~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.14/site-packages/datasets/arrow_writer.py", line 773, in _write_table
pa_table = table_cast(pa_table, self._schema)
File "/usr/local/lib/python3.14/site-packages/datasets/table.py", line 2369, in table_cast
return cast_table_to_schema(table, schema)
File "/usr/local/lib/python3.14/site-packages/datasets/table.py", line 2297, in cast_table_to_schema
raise CastError(
...<3 lines>...
)
datasets.table.CastError: Couldn't cast
year: int64
election_type: string
party: string
alliance: string
seats_contested: string
seats_won: int64
notes: string
-- schema metadata --
pandas: '{"index_columns": [{"kind": "range", "name": null, "start": 0, "' + 1090
to
{'district': Value('string'), 'total_ac': Value('int64'), 'tvk_seats': Value('int64'), 'dmk_seats': Value('int64'), 'admk_seats': Value('int64'), 'inc_seats': Value('int64'), 'pmk_seats': Value('int64'), 'vck_seats': Value('int64'), 'cpi_seats': Value('int64'), 'cpim_seats': Value('int64'), 'iuml_seats': Value('int64'), 'bjp_seats': Value('int64'), 'dmdk_seats': Value('int64'), 'ammk_seats': Value('int64'), 'other_seats': Value('int64'), 'source': Value('string')}
because column names don't match
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/src/services/worker/src/worker/job_runners/config/parquet_and_info.py", line 1369, in compute_config_parquet_and_info_response
parquet_operations, partial, estimated_dataset_info = stream_convert_to_parquet(
~~~~~~~~~~~~~~~~~~~~~~~~~^
builder, max_dataset_size_bytes=max_dataset_size_bytes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/src/services/worker/src/worker/job_runners/config/parquet_and_info.py", line 948, in stream_convert_to_parquet
builder._prepare_split(split_generator=splits_generators[split], file_format="parquet")
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.14/site-packages/datasets/builder.py", line 1683, in _prepare_split
for job_id, done, content in self._prepare_split_single(
~~~~~~~~~~~~~~~~~~~~~~~~~~^
gen_kwargs=gen_kwargs, job_id=job_id, **_prepare_split_args
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
):
^
File "/usr/local/lib/python3.14/site-packages/datasets/builder.py", line 1839, in _prepare_split_single
raise DatasetGenerationCastError.from_cast_error(
...<4 lines>...
)
datasets.exceptions.DatasetGenerationCastError: An error occurred while generating the dataset
All the data files must have the same columns, but at some point there are 7 new columns ({'seats_won', 'election_type', 'notes', 'alliance', 'party', 'year', 'seats_contested'}) and 16 missing columns ({'admk_seats', 'inc_seats', 'iuml_seats', 'total_ac', 'cpim_seats', 'cpi_seats', 'dmdk_seats', 'source', 'vck_seats', 'district', 'dmk_seats', 'pmk_seats', 'ammk_seats', 'other_seats', 'bjp_seats', 'tvk_seats'}).
This happened while the csv dataset builder was generating data using
hf://datasets/ThinkPolitically/tamil-nadu-election-data/tn_election_party_results_2011_2026.csv (at revision 34bf6d8222cb5b4117d4f7994774567a82e8254b), ['hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_district_vote_share_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_election_party_results_2011_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_swing_constituencies_2011_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_tvk_booth_organisation_2026.csv', 'hf://datasets/ThinkPolitically/tamil-nadu-election-data@34bf6d8222cb5b4117d4f7994774567a82e8254b/tn_youth_turnout_2026.csv']
Please either edit the data files to have matching columns, or separate them into different configurations (see docs at https://hf.co/docs/hub/datasets-manual-configuration#multiple-configurations)Need help to make the dataset viewer work? Make sure to review how to configure the dataset viewer, and open a discussion for direct support.
district string | total_ac int64 | tvk_seats int64 | dmk_seats int64 | admk_seats int64 | inc_seats int64 | pmk_seats int64 | vck_seats int64 | cpi_seats int64 | cpim_seats int64 | iuml_seats int64 | bjp_seats int64 | dmdk_seats int64 | ammk_seats int64 | other_seats int64 | source string |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Ariyalur | 2 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Chengalpattu | 7 | 5 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Chennai | 16 | 14 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Coimbatore | 10 | 6 | 3 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Cuddalore | 9 | 1 | 3 | 3 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | tnelections2026.in |
Dharmapuri | 5 | 1 | 0 | 3 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Dindigul | 7 | 1 | 4 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Erode | 8 | 5 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Kallakurichi | 4 | 1 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Kancheepuram | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Kanniyakumari | 6 | 0 | 1 | 1 | 3 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Karur | 4 | 1 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Krishnagiri | 6 | 2 | 1 | 2 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Madurai | 10 | 8 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Mayiladuthurai | 3 | 0 | 2 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Nagapattinam | 3 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Namakkal | 6 | 5 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Perambalur | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Pudukkottai | 6 | 2 | 3 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Ramanathapuram | 4 | 1 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Ranipet | 4 | 3 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Salem | 11 | 4 | 0 | 7 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Sivaganga | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tenkasi | 5 | 0 | 4 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Thanjavur | 8 | 2 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | tnelections2026.in |
The Nilgiris | 3 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | tnelections2026.in |
Theni | 4 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Thiruvallur | 10 | 9 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Thiruvarur | 4 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | tnelections2026.in |
Thoothukudi | 6 | 3 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tiruchirappalli | 9 | 6 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tirunelveli | 5 | 3 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tirupathur | 4 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tiruppur | 8 | 4 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Tiruvannamalai | 8 | 1 | 2 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Vellore | 5 | 4 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Viluppuram | 7 | 0 | 2 | 2 | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
Virudhunagar | 7 | 4 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | tnelections2026.in |
null | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
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null | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Coimbatore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Coimbatore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Coimbatore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Madurai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Madurai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Chennai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Thoothukudi | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Thoothukudi | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Ranipet | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Vellore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruvannamalai | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Villupuram | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Cuddalore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Cuddalore | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Thanjavur | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Thanjavur | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Thanjavur | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruchirappalli | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruchirappalli | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruchirappalli | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Namakkal | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Namakkal | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Salem | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Salem | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Erode | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Erode | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruppur | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
Tiruppur | null | null | null | null | null | null | null | null | null | null | null | null | null | null | null |
End of preview.
Tamil Nadu Legislative Assembly Election Dataset 2011–2026
Compiled by: ThinkPolitically — Tamil Nadu's election campaign and political strategy consultancy
License: CC-BY-4.0 (free to use with attribution)
Last updated: July 2026
Citation URL: https://thinkpolitically.com/tamil-nadu-election-report-2026/
Dataset Description
The most granular publicly available dataset on Tamil Nadu state assembly elections, covering four election cycles (2011, 2016, 2021, 2026) across all 234 constituencies. Includes party-level vote share, swing constituency classification, booth organisation quality scores, district-level breakdowns, and youth voter turnout analysis.
Key Findings in the Data
- TVK's 2026 debut — 108 seats, 34.92% vote share on solo contest: the largest first-election seat count by any party in post-1967 Tamil Nadu history
- Dravidian duopoly collapse — DMK + AIADMK combined share fell from ~76% (2016) to ~45% (2026): lowest since 1971
- Booth organisation gap — TVK won 91% of constituencies with complete booth coverage vs 12% with thin coverage; 68 thin-coverage constituencies are the primary structural reason TVK fell short of a majority
- Youth turnout differential — First-time voter (18–25) turnout was 7.3 percentage points higher in TVK-won constituencies vs TVK-lost constituencies
- 38 swing seats — Constituencies that changed hands at least twice between 2011–2021; split 22 TVK / 11 DMK / 5 AIADMK in 2026
Files in This Dataset
| File | Description | Rows |
|---|---|---|
tn_election_party_results_2011_2026.csv |
Party-level results: seats contested, seats won, vote share, alliance — 4 elections | 22 |
tn_swing_constituencies_2011_2026.csv |
38 swing constituencies with winner, party, and margin data per election cycle | 38 |
tn_tvk_booth_organisation_2026.csv |
TVK's booth organisation quality (Complete/Partial/Thin) vs win rate in 2026 | 3 |
tn_district_vote_share_2026.csv |
District-level vote share estimates and seat counts for all 38 TN districts in 2026 | 38 |
tn_youth_turnout_2026.csv |
First-time voter turnout in TVK-won vs TVK-lost constituencies | 3 |
Data Sources
- Election Commission of India — Official results for 2011, 2016, and 2021 elections (seats, vote share, margins)
- ThinkPolitically field research — 47-constituency field survey (February–April 2026): booth organisation quality, candidate interviews, voter contact logs
- Partial ECI 2026 returns — Declared results as of June 15, 2026; vote share figures for 2026 marked as estimates pending final ECI publication
Note on 2026 data: Final constituency-level ECI data for 2026 was not fully published at dataset compilation. Seat counts are based on declared results. Vote share percentages are ThinkPolitically estimates derived from partial returns and field data. All 2026 figures should be treated as preliminary until ECI publishes final results.
Methodology Notes
Swing Constituency Classification
A constituency is classified as a swing seat if it meets all three criteria:
- Changed hands between at least two consecutive election cycles (2011–2016 or 2016–2021)
- Winning margin was below 8,000 votes in at least two of the three elections (2011, 2016, 2021)
- No single party won with more than 12% vote-share advantage in any of the three elections
Booth Organisation Classification (2026 Field Data)
A constituency is classified as Complete if TVK had: (a) a polling agent at every booth, (b) a voter roll marked to household level, (c) a transport coordinator, and (d) a local party contact on election day. Partial = 50–99% of booths met all four criteria. Thin = fewer than 50% of booths met two or more criteria.
Youth Turnout Data
First-time voter (18–25) turnout figures are from ThinkPolitically's field survey sample (47 constituencies). State-level figures are extrapolated estimates; constituency-level variation is not captured in this dataset.
Suggested Use Cases
- Political science research on Indian state elections
- Machine learning models for election outcome prediction
- Visualisation of Tamil Nadu's shifting political landscape 2011–2026
- Comparative study of booth-level organisation vs electoral outcomes
- Analysis of youth voter mobilisation in Indian elections
Citation
If you use this dataset, please cite:
ThinkPolitically (2026). Tamil Nadu Legislative Assembly Election Dataset 2011–2026.
Retrieved from https://huggingface.co/datasets/thinkpolitically/tamil-nadu-election-data
Original research report: https://thinkpolitically.com/tamil-nadu-election-report-2026/
License: CC-BY-4.0
About ThinkPolitically
ThinkPolitically is Tamil Nadu's specialist election campaign management and political strategy consultancy, based in Chennai. We provide constituency analysis, voter data research, campaign strategy, and field operations for Tamil Nadu state and national elections.
Contact: thinkpolitically.com/contact
Services: Election Campaign Management | Voter Analysis | Political Strategy
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