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【pandas】文字列をDataFrameに展開

Posted at

かゆいところに手が届くpandasレシピ集No.1

かゆいこと

「カテゴリ名(index)」と「値(value)」が文字列として1つの要素となってしまっている配列・DataFrameをなんとかしたい。
各カテゴリ(index)をcolumn名とする列に値を割り振ろう。

ID クソデカ文字列
0 A 0, B 1, C 2
1 B 3, D 4
2 A 5, C 6
3 C 7, D 8

↑この↑クソデカ文字列を↓こう↓したい。

ID A B C D
0 0 1 2 0
1 0 3 0 4
2 5 0 6 0
3 0 0 7 8

レシピ

各カテゴリは既知とします。
未知の場合、カテゴリのリストを作成してください。

str_to_dataframe.py
import numpy as np
import pandas as pd

def str_to_dict(x):
    dic = {'A' : 0, 'B' : 0, 'C' : 0, 'D' : 0}
    for xx in x.split(","):
        xxs = xx.split(" ")
        dic[xxs[-2]] = int(xxs[-1])
    return dic

temp = df["クソデカ文字列"].apply(lambda x : pd.Series(str_to_dataframe(x)))
df = pd.concat((df, temp), axis=1)

これは早い!

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