DOC: defaults in read_parquet parameters#7567
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April 16, 2021 16:56
jsignell
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Apr 26, 2021
| filtering is only performed at the partition level, i.e., to prevent the | ||
| loading of some row-groups and/or files. | ||
| filters : Union[List[Tuple[str, str, Any]], List[List[Tuple[str, str, Any]]]], default None | ||
| List of filters to apply, like ``[[('col1', '==', 0), ...], ...]``. |
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Does it really need ==? Seems like it works fine with just the = locally.
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Good Q. I believe so. Here's some code to test (taken from https://sites.google.com/view/raybellwaves/blog/read_parquetcar-parquet-enginevroom)
import pandas as pd
import dask.dataframe as dd
df = pd.DataFrame({'x': [0, 1]})
ddf = dd.from_pandas(df, npartitions=2)
ddf.to_parquet("dd_df.parquet", engine="pyarrow")
dd.read_parquet("dd_df.parquet", engine="pyarrow-dataset", filters=[[('x', '=', 0)]]).compute() # returns empty
dd.read_parquet("dd_df.parquet", engine="pyarrow-dataset", filters=[[('x', '=', 0)]]).compute() # returns filtered data
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Oh huh. I guess the one I was testing on was filtered at the file-level, and it seemed to work the same. Thanks for writing this out!
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Added in defaults and tidied up the filters example