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Write a JSON file from a Dataframe in Pola-rs

Starting with a DataFrame that has a form such as this

df = pl.DataFrame([{"SkuId":1}])
shape: (1, 1)
┌───────┐
│ SkuId │
│ ---   │
│ i64   │
╞═══════╡
│ 1     │
└───────┘

How can I write it to a JSON file with this format?

"SkuId": {"source": 1},
Tags:

2

Answers


  1. 0

    You can first transform the Polars DataFrame to a dictionary and then manipulate the dictionary to match the format you want before writing it to a JSON file.

    import polars as pl
import json

# Create the Polars DataFrame
df = pl.DataFrame([{"SkuId": 1}])

# Convert the DataFrame to a dictionary
df_dict = df.to_dict(as_series=False)

# Transform to the desired format
output_dict = {key: {"source": value[0]} for key, value in df_dict.items()}

# Write to a JSON file
with open('output.json', 'w') as f:
    json.dump(output_dict, f, indent=4)

print(output_dict)
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  2. 0

    Polars has two (really 3) nested types. There are Structs which are like objects (aka {}) in JSON and Lists which are like Arrays (aka []).

    To get it to put JSON in the format you’re looking for, you need to make a struct.

    df.select(SkuId=pl.struct(source=pl.col('SkuId'))).write_json()

[{"SkuId":{"source":1}}]

    Of course, if you put a file path inside write_json() then it’ll write it to the file instead of just printing it to stdout.

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