在大 pandas DataFrame中获取非空元素 [英] Get non-null elements in a pandas DataFrame

问题描述

我有一个 DataFrame ，我想得到一些非空元素作为列表。

I have a DataFrame and I want to get some non-null elements as a list.

具体给定 df ：

df = pd.DataFrame({"a":["A",None,"B"],"b":[None,"C","D"],"c":["E","F",None]})
      a     b     c
0     A  None     E
1  None     C     F
2     B     D  None

和有趣的列列表 [a，c] ，我想提取非 - 无元素指定列，即

and the interesting columns list ["a","c"], I want to extract the list of non-None element of the specified columns, i.e.,

["A","B","E","F"]

我想我可以做

[value for colname in interesting_columns
 for value in df.loc[df[colname].notnull(),colname]]

但我想知道是否有一些非迭代的魔术。

but I was wondering if there is some non-iterative magic trick.

推荐答案

您可以 stack 它长格式并使用 .values 访问者。默认情况下， stack（）自动丢失值：

You can stack it to long format and retrieve the data with .values accessor. By default, stack() drops missing values automatically:

df[['a', 'c']].T.stack().values
# array(['A', 'B', 'E', 'F'], dtype=object)

---

或者如果你想要一个列表：

---

Or if you want a list:

df[['a', 'c']].T.stack().tolist()
# ['A', 'B', 'E', 'F']

---

T 需要按照您要求的顺序获取值。

---

T is needed to get the values in the order you requested.

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