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GH-32320: [R] Docs unclear about potential disadvantages of dictionary encoding #50093

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GH-32320: [R] Docs unclear about potential disadvantages of dictionary encoding #50093

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2 changes: 2 additions & 0 deletions python/pyarrow/parquet/core.py
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Expand Up @@ -769,6 +769,8 @@ def _sanitize_table(table, new_schema, flavor):
When encoding the column, if the dictionary size is too large, the
column will fallback to ``PLAIN`` encoding. Specially, ``BOOLEAN`` type
doesn't support dictionary encoding.
On columns with many unique values, dictionary encoding can increase
file size and reduce compression effectiveness.
compression : str or dict, default 'snappy'
Specify the compression codec, either on a general basis or per-column.
Valid values: {'NONE', 'SNAPPY', 'GZIP', 'BROTLI', 'LZ4', 'LZ4_RAW', 'ZSTD'}.
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4 changes: 3 additions & 1 deletion r/R/parquet.R
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Expand Up @@ -106,7 +106,9 @@ read_parquet <- function(
#' @param compression compression algorithm. Default "snappy". See details.
#' @param compression_level compression level. Meaning depends on compression
#' algorithm
#' @param use_dictionary logical: use dictionary encoding? Default `TRUE`
#' @param use_dictionary logical: use dictionary encoding? Default `TRUE`.
#' On columns with many unique values, dictionary encoding can increase
#' file size and reduce compression effectiveness.
#' @param write_statistics logical: include statistics? Default `TRUE`
#' @param data_page_size Set a target threshold for the approximate encoded
#' size of data pages within a column chunk (in bytes). Default 1 MiB.
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