pandas df.apply不修改DataFrame [英] Pandas df.apply does not modify DataFrame

问题描述

我刚开始做熊猫，所以如果这太愚蠢，请原谅.

I am just starting pandas so please forgive if this is something stupid.

我正在尝试将函数应用于列，但是它不起作用，并且我也没有看到任何错误.

I am trying to apply a function to a column but its not working and i don't see any errors also.

 capitalizer = lambda x: x.upper()
    for df in pd.read_csv(downloaded_file, chunksize=2, compression='gzip', low_memory=False):
        df['level1'].apply(capitalizer)
        print df
        exit(1)

此打印显示的 level1 列值与原始csv相同，而不执行 upper .我在这里想念什么吗?

This print shows the level1 column values same as the original csv not doing upper. Am i missing something here ?

谢谢

推荐答案

apply 不是 inplace 函数-它不会修改原始对象中的值，因此您需要将其分配回去:

apply is not an inplace function - it does not modify values in the original object, so you need to assign it back:

df['level1'] = df['level1'].apply(capitalizer)

---

或者，您可以使用 str.upper ，它应该快得多.

df['level1'] = df['level1'].str.upper()

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