pandas 数据框:截断字符串字段 [英] Pandas dataframe: truncate string fields

问题描述

我有一个数据框，想将每个字段截断为最多20个字符.我一直在天真地尝试以下操作:

I have a dataframe and would like to truncate each field to up to 20 characters. I've been naively trying the following:

df = df.astype(str).apply(lambda x: x[:20])

但是它没有任何作用.但是，如果我想在每个字段中添加一个"Y"，则它就像一个超级按钮:

however it has no effect whatsoever. If, however, I wanted to add an 'Y' to each field, this works like a charm:

df = df.astype(str).apply(lambda x: x+'Y')

我在做什么错了?

推荐答案

，您可以使用演示:

In [177]: df = pd.DataFrame({
     ...:   'a': pd.util.testing.rands_array(30, 10),
     ...:   'b': pd.util.testing.rands_array(30, 10),
     ...: })
     ...:

In [178]: df
Out[178]:
                                a                               b
0  Mlf6nOsC8S6vv8OxW5ZOWifg3EoqAb  XSGLdkaewwZlNeZ4uTTivi2nMQFc6S
1  0E4XCBaYFBTSalUMPGpXmke6dQGbkW  KlHuVhbNgQL9HLHYQq3fEdqEIciOhX
2  URODJeLA0uLvcKBEXPyrmnnNU40MDl  NaY8LURHjgmT1pRrDnbPAeLZq3ANaL
3  OYA1ahlwVtEVnDOAkZgxNkbvZ7W8Rf  mIzkeLhM7SqYH17vGDzL6DJjSYftGs
4  uFC1shE02UfxS0VhDASmF8vh9XxFYX  fQOxjDjFehTNT27seOtCAAPW0as9Up
5  Ja33vQym6L0Ko2Kcf8cg7OMBKMitg5  iGdCvYTyZlR23NeeTAjG1PoL8mWm3j
6  iNZdXaVpB4zXClxTLt738DY7i6xs6p  q9VKg5fZdItmUpZiQrR6XW5WHmd33l
7  WWnViRRMPkbXNQOHeqGmzETDpGPRl9  t3I8Ve3ybCJcXajF8pydnwNZQWslTN
8  5oMFy2PBe1zUIE3XdraMwlrd5MKcx2  gSLtgXJwiS1HugLORXherFT4l1k5QV
9  weV8BlyJrtRbWpSCxSbj8cSyZxusFR  ylLWort9o8mHWQQ3JB1Twb0xRbLhot

In [179]: df.apply(lambda x: x.str.slice(0, 20))
Out[179]:
                      a                     b
0  Mlf6nOsC8S6vv8OxW5ZO  XSGLdkaewwZlNeZ4uTTi
1  0E4XCBaYFBTSalUMPGpX  KlHuVhbNgQL9HLHYQq3f
2  URODJeLA0uLvcKBEXPyr  NaY8LURHjgmT1pRrDnbP
3  OYA1ahlwVtEVnDOAkZgx  mIzkeLhM7SqYH17vGDzL
4  uFC1shE02UfxS0VhDASm  fQOxjDjFehTNT27seOtC
5  Ja33vQym6L0Ko2Kcf8cg  iGdCvYTyZlR23NeeTAjG
6  iNZdXaVpB4zXClxTLt73  q9VKg5fZdItmUpZiQrR6
7  WWnViRRMPkbXNQOHeqGm  t3I8Ve3ybCJcXajF8pyd
8  5oMFy2PBe1zUIE3XdraM  gSLtgXJwiS1HugLORXhe
9  weV8BlyJrtRbWpSCxSbj  ylLWort9o8mHWQQ3JB1T

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