在pandas DataFrame的每一列中查找第一个非零值 [英] Find first non-zero value in each column of pandas DataFrame

问题描述

在数据框的每一列(从上到下)中获取第一个非零元素的值和索引的潘多拉式方法是什么?

What is a pandoric way to get a value and index of the first non-zero element in each column of a DataFrame (top to bottom)?

import pandas as pd

df = pd.DataFrame([[0, 0, 0],
                   [0, 10, 0],
                   [4, 0, 0],
                   [1, 2, 3]],
                  columns=['first', 'second', 'third'])

print(df.head())

#    first  second  third
# 0      0       0      0
# 1      0      10      0
# 2      4       0      0
# 3      1       2      3

我想要实现的目标:

#        value  pos
# first      4    2
# second    10    1
# third      1    3

推荐答案

您正在寻找

You're looking for idxmax which gives you the first position of the maximum. However, you need to find the max of "not equal to zero"

df.ne(0).idxmax()

first     2
second    1
third     3
dtype: int64

---

我们可以将其与 lookup 和 assign

---

We can couple this with lookup and assign

df.ne(0).idxmax().to_frame('pos').assign(val=lambda d: df.lookup(d.pos, d.index))

        pos  val
first     2    4
second    1   10
third     3    3

---

相同答案的包装略有不同.

---

Same answer packaged slightly differently.

m = df.ne(0).idxmax()
pd.DataFrame(dict(pos=m, val=df.lookup(m, m.index)))

        pos  val
first     2    4
second    1   10
third     3    3

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