Python Pandas:在所有单元格中选择数组中的第一个元素 [英] Python Pandas: selecting 1st element in array in all cells

问题描述

我想做的是选择每个单元格的第一个元素，而不考虑列或行的数量(它们可能会根据用户定义的标准而改变)，并从数据中创建一个新的pandas数据框.我的实际数据结构与下面列出的类似.

What I am trying to do is select the 1st element of each cell regardless of the number of columns or rows (they may change based on user defined criteria) and make a new pandas dataframe from the data. My actual data structure is similar to what I have listed below.

       0       1       2
0   [1, 2]  [2, 3]  [3, 6]
1   [4, 2]  [1, 4]  [4, 6]
2   [1, 2]  [2, 3]  [3, 6]
3   [4, 2]  [1, 4]  [4, 6]

我希望新的数据框看起来像这样:

I want the new dataframe to look like:

    0   1   2
0   1   2   3
1   4   1   4
2   1   2   3
3   4   1   4

下面的代码生成一个类似于我的数据集，并尝试在我的代码中做我想做的但没有成功的数据(d)，并且模仿了我在类似的问题中看到的成功(c)的情况；但是，只有一个柱子).指向类似但不同的问题的链接在这里: Python Pandas:在其中选择元素数组列

The code below generates a data set similar to mine and attempts to do what I want to do in my code without success (d), and mimics what I have seen in a similar question with success(c ; however, only one column). The link to the similar, but different question is here :Python Pandas: selecting element in array column

import pandas as pd

zz = pd.DataFrame([[[1,2],[2,3],[3,6]],[[4,2],[1,4],[4,6]],
               [[1,2],[2,3],[3,6]],[[4,2],[1,4],[4,6]]])
print(zz)

x= zz.dtypes
print(x)

a = pd.DataFrame((zz.columns.values))
b = pd.DataFrame.transpose(a) 
c =zz[0].str[0] # this will give the 1st value for each cell in columns 0
d= zz[[b[0]].values].str[0] #attempt to get 1st value for each cell in all columns

推荐答案

您可以使用apply，并使用使用 stack 的另一种解决方案和 unstack :

print (zz.stack().str[0].unstack())
   0  1  2
0  1  2  3
1  4  1  4
2  1  2  3
3  4  1  4

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