Read a page from a Parquet file

Usage

read_parquet_page(file, offset)

Arguments

file: Path to a Parquet file.
offset: Integer offset of the start of the page in the file. See parquet_pages() for a list of all pages and their offsets.

Value

Named list. Many entries correspond to the columns of the result of parquet_pages(). Additional entries are:

codec: compression codec. Possible values:
has_repetition_levels: whether the page has repetition levels.
has_definition_levels: whether the page has definition levels.
schema_column: which schema column the page corresponds to. Note that only leaf columns have pages.
data_type: low level Parquet data type. Possible values:
repetition_type: whether the column the page belongs to is REQUIRED, OPTIONAL or REPEATED.
page_header: the bytes of the page header in a raw vector.
num_null: number of missing (NA) values. Only set in V2 data pages.
num_rows: this is the same as num_values for flat tables, i.e. files without repetition levels.
compressed_data: the data of the page in a raw vector. It includes repetition and definition levels, if any.
data: the uncompressed data, if nanoparquet supports the compression codec of the file (GZIP and SNAPPY at the time of writing), or if the file is not compressed. In the latter case it is the same as compressed_data.

Examples

file_name <- system.file("extdata/userdata1.parquet", package = "nanoparquet")
nanoparquet:::parquet_pages(file_name)
#> # A data frame: 19 × 14
#>    file_name                 row_group column page_type page_header_offset
#>    <chr>                         <int>  <int> <chr>                  <dbl>
#>  1 /home/runner/work/_temp/…         0      0 DATA_PAGE                  4
#>  2 /home/runner/work/_temp/…         0      1 DATA_PAGE               6741
#>  3 /home/runner/work/_temp/…         0      2 DICTIONA…              10766
#>  4 /home/runner/work/_temp/…         0      2 DATA_PAGE              12259
#>  5 /home/runner/work/_temp/…         0      3 DICTIONA…              13334
#>  6 /home/runner/work/_temp/…         0      3 DATA_PAGE              15211
#>  7 /home/runner/work/_temp/…         0      4 DATA_PAGE              16239
#>  8 /home/runner/work/_temp/…         0      5 DICTIONA…              31726
#>  9 /home/runner/work/_temp/…         0      5 DATA_PAGE              31759
#> 10 /home/runner/work/_temp/…         0      6 DATA_PAGE              32031
#> 11 /home/runner/work/_temp/…         0      7 DATA_PAGE              42952
#> 12 /home/runner/work/_temp/…         0      8 DICTIONA…              53749
#> 13 /home/runner/work/_temp/…         0      8 DATA_PAGE              55009
#> 14 /home/runner/work/_temp/…         0      9 DATA_PAGE              55925
#> 15 /home/runner/work/_temp/…         0     10 DATA_PAGE              59312
#> 16 /home/runner/work/_temp/…         0     11 DICTIONA…              65063
#> 17 /home/runner/work/_temp/…         0     11 DATA_PAGE              67026
#> 18 /home/runner/work/_temp/…         0     12 DICTIONA…              68019
#> 19 /home/runner/work/_temp/…         0     12 DATA_PAGE              71089
#> # ℹ 9 more variables: uncompressed_page_size <int>,
#> #   compressed_page_size <int>, crc <int>, num_values <int>,
#> #   encoding <chr>, definition_level_encoding <chr>,
#> #   repetition_level_encoding <chr>, data_offset <dbl>,
#> #   page_header_length <int>
options(max.print = 100)  # otherwise long raw vector
nanoparquet:::read_parquet_page(file_name, 4L)
#> $page_type
#> [1] "DATA_PAGE"
#> 
#> $row_group
#> [1] 0
#> 
#> $column
#> [1] 0
#> 
#> $page_header_offset
#> [1] 4
#> 
#> $data_page_offset
#> [1] 24
#> 
#> $page_header_length
#> [1] 20
#> 
#> $compressed_page_size
#> [1] 6717
#> 
#> $uncompressed_page_size
#> [1] 8000
#> 
#> $codec
#> [1] "SNAPPY"
#> 
#> $num_values
#> [1] 1000
#> 
#> $encoding
#> [1] "PLAIN"
#> 
#> $definition_level_encoding
#> [1] "PLAIN"
#> 
#> $repetition_level_encoding
#> [1] "PLAIN"
#> 
#> $has_repetition_levels
#> [1] FALSE
#> 
#> $has_definition_levels
#> [1] FALSE
#> 
#> $schema_column
#> [1] 1
#> 
#> $data_type
#> [1] "INT64"
#> 
#> $repetition_type
#> [1] "REQUIRED"
#> 
#> $page_header
#>  [1] 15 00 15 80 7d 15 fa 68 2c 15 d0 0f 15 00 15 00 15 00 00 00
#> 
#> $data
#>   [1] 40 be 0c f1 d8 2a 05 00 c0 86 e0 9a e0 2a 05 00 c0 28 33 45 d3 2a 05
#>  [24] 00 40 2b 96 ce d2 2a 05 00 c0 9c 33 91 d6 2a 05 00 80 a2 54 7b d8 2a
#>  [47] 05 00 00 59 b2 77 d9 2a 05 00 80 ee 7d fc d7 2a 05 00 40 cf 71 8d d5
#>  [70] 2a 05 00 c0 bc 7b cd e1 2a 05 00 80 e4 da 72 d2 2a 05 00 80 30 4d 73
#>  [93] e1 2a 05 00 40 fe a4 0f
#>  [ reached getOption("max.print") -- omitted 7900 entries ]
#> 
#> $definition_levels_byte_length
#> [1] NA
#> 
#> $repetition_levels_byte_length
#> [1] NA
#> 
#> $num_nulls
#> [1] NA
#> 
#> $num_rows
#> [1] NA
#> 
#> $compressed_data
#>   [1] c0 3e 30 40 be 0c f1 d8 2a 05 00 c0 86 e0 9a e0 01 08 2c 28 33 45 d3
#>  [24] 2a 05 00 40 2b 96 ce d2 01 10 28 9c 33 91 d6 2a 05 00 80 a2 54 7b 01
#>  [47] 28 10 00 59 b2 77 d9 01 10 0c ee 7d fc d7 01 28 0c cf 71 8d d5 01 28
#>  [70] 0c bc 7b cd e1 01 18 08 e4 da 72 01 38 0c 80 30 4d 73 01 10 30 40 fe
#>  [93] a4 0f e2 2a 05 00 00 eb
#>  [ reached getOption("max.print") -- omitted 6617 entries ]
#>

Read a page from a Parquet file

Usage

Arguments

Value

See also

Examples