github.com/apache/arrow/go/v14@v14.0.1/parquet/cmd/parquet_reader/README.md

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# parquet\_reader

A tool to read Parquet files and write selected columns into TEXT, JSON, or CSV files.

## Usage

```
$ ./parquet_reader -h
Parquet Reader (version 0.1.20220629.1846)
Usage:
  parquet_reader -h | --help
  parquet_reader [--only-metadata] [--no-metadata] [--no-memory-map] [--json] [--csv] [--output=FILE]
                 [--print-key-value-metadata] [--int96-timestamp] [--columns=COLUMNS] <file>
Options:
  -h --help                     Show this screen.
  --print-key-value-metadata    Print out the key-value metadata. [default: false]
  --only-metadata               Stop after printing metadata, no values.
  --no-metadata                 Do not print metadata.
  --output=FILE                 Specify output file for data. [default: -]
  --no-memory-map               Disable memory mapping the file.
  --int96-timestamp             Parse INT96 as TIMESTAMP for legacy support.
  --json                        Format output as JSON instead of text.
  --csv                         Format output as CSV instead of text.
  --columns=COLUMNS             Specify a subset of columns to print, comma delimited indexes.
```

# Examples

## Text
```
$ ./parquet_reader --no-metadata v0.7.1.parquet
carat             |cut               |color             |clarity           |depth             |table             |price             |x                 |y                 |z                 |__index_level_0__ |
0.230000          |Ideal             |E                 |SI2               |61.500000         |55.000000         |326               |3.950000          |3.980000          |2.430000          |0                 |
0.210000          |Premium           |E                 |SI1               |59.800000         |61.000000         |326               |3.890000          |3.840000          |2.310000          |1                 |
0.230000          |Good              |E                 |VS1               |56.900000         |65.000000         |327               |4.050000          |4.070000          |2.310000          |2                 |
0.290000          |Premium           |I                 |VS2               |62.400000         |58.000000         |334               |4.200000          |4.230000          |2.630000          |3                 |
0.310000          |Good              |J                 |SI2               |63.300000         |58.000000         |335               |4.340000          |4.350000          |2.750000          |4                 |
0.240000          |Very Good         |J                 |VVS2              |62.800000         |57.000000         |336               |3.940000          |3.960000          |2.480000          |5                 |
0.240000          |Very Good         |I                 |VVS1              |62.300000         |57.000000         |336               |3.950000          |3.980000          |2.470000          |6                 |
0.260000          |Very Good         |H                 |SI1               |61.900000         |55.000000         |337               |4.070000          |4.110000          |2.530000          |7                 |
0.220000          |Fair              |E                 |VS2               |65.100000         |61.000000         |337               |3.870000          |3.780000          |2.490000          |8                 |
0.230000          |Very Good         |H                 |VS1               |59.400000         |61.000000         |338               |4.000000          |4.050000          |2.390000          |9                 |
```

## JSON
```
$ ./parquet_reader --no-metadata --json v0.7.1.parquet
[{"carat":0.23,"cut":"Ideal","color":"E","clarity":"SI2","depth":61.5,"table":55,"price":326,"x":3.95,"y":3.98,"z":2.43,"__index_level_0__":0},{"carat":0.21,"cut":"Premium","color":"E","clarity":"SI1","depth":59.8,"table":61,"price":326,"x":3.89,"y":3.84,"z":2.31,"__index_level_0__":1},{"carat":0.23,"cut":"Good","color":"E","clarity":"VS1","depth":56.9,"table":65,"price":327,"x":4.05,"y":4.07,"z":2.31,"__index_level_0__":2},{"carat":0.29,"cut":"Premium","color":"I","clarity":"VS2","depth":62.4,"table":58,"price":334,"x":4.2,"y":4.23,"z":2.63,"__index_level_0__":3},{"carat":0.31,"cut":"Good","color":"J","clarity":"SI2","depth":63.3,"table":58,"price":335,"x":4.34,"y":4.35,"z":2.75,"__index_level_0__":4},{"carat":0.24,"cut":"Very Good","color":"J","clarity":"VVS2","depth":62.8,"table":57,"price":336,"x":3.94,"y":3.96,"z":2.48,"__index_level_0__":5},{"carat":0.24,"cut":"Very Good","color":"I","clarity":"VVS1","depth":62.3,"table":57,"price":336,"x":3.95,"y":3.98,"z":2.47,"__index_level_0__":6},{"carat":0.26,"cut":"Very Good","color":"H","clarity":"SI1","depth":61.9,"table":55,"price":337,"x":4.07,"y":4.11,"z":2.53,"__index_level_0__":7},{"carat":0.22,"cut":"Fair","color":"E","clarity":"VS2","depth":65.1,"table":61,"price":337,"x":3.87,"y":3.78,"z":2.49,"__index_level_0__":8},{"carat":0.23,"cut":"Very Good","color":"H","clarity":"VS1","depth":59.4,"table":61,"price":338,"x":4,"y":4.05,"z":2.39,"__index_level_0__":9}]
```

## CSV
```
$ ./parquet_reader --no-metadata --csv v0.7.1.parquet
"carat","cut","color","clarity","depth","table","price","x","y","z","__index_level_0__"
0.23,"Ideal","E","SI2",61.5,55,326,3.95,3.98,2.43,0
0.21,"Premium","E","SI1",59.8,61,326,3.89,3.84,2.31,1
0.23,"Good","E","VS1",56.9,65,327,4.05,4.07,2.31,2
0.29,"Premium","I","VS2",62.4,58,334,4.2,4.23,2.63,3
0.31,"Good","J","SI2",63.3,58,335,4.34,4.35,2.75,4
0.24,"Very Good","J","VVS2",62.8,57,336,3.94,3.96,2.48,5
0.24,"Very Good","I","VVS1",62.3,57,336,3.95,3.98,2.47,6
0.26,"Very Good","H","SI1",61.9,55,337,4.07,4.11,2.53,7
0.22,"Fair","E","VS2",65.1,61,337,3.87,3.78,2.49,8
0.23,"Very Good","H","VS1",59.4,61,338,4,4.05,2.39,9
```

## Write JSON to output file
```
$ ./parquet_reader --no-metadata --json --output=data.json v0.7.1.parquet
$ jq . data.json
[
  {
    "carat": 0.23,
    "cut": "Ideal",
    "color": "E",
    "clarity": "SI2",
    "depth": 61.5,
    "table": 55,
    "price": 326,
    "x": 3.95,
...
```

## Write CSV to output file
```
$ ./parquet_reader --no-metadata --csv --output=data.csv v0.7.1.parquet
```