How do I fill a column with one value in Pandas?

Question

I have a column with consecutive digits in a Pandas DataFrame.

A
1
2
3
4

I would like to change all those values to a simple string, say "foo", resulting in

A
foo
foo
foo
foo

Answer 1

Just select the column and assign like normal:

In [194]:
df['A'] = 'foo'
df

Out[194]:
     A
0  foo
1  foo
2  foo
3  foo

Assigning a scalar value will set all the rows to the same scalar value

Answer 2

The good answer above throws a warning. You can also do:

df.insert(0, 'A', 'foo')

where 0 is the index where the new column will be inserted.

Answer 3

You can also exploit the power of the .loc property by addressing all the rows using : as the argument. Say that your DataFrame is called df :

df.loc[:,'A'] = 'foo'

Resulting in

     A
0  foo
1  foo
2  foo
3  foo

Answer 4

您可以使用方法assign ：

df = df.assign(A='foo')

Answer 5

You could also try pd.Series.replace :

df['A'] = df['A'].replace(df['A'], 'foo')
print(df)

Output:

     A
0  foo
1  foo
2  foo
3  foo

Answer 6

要使其在不收到切片错误/警告的情况下工作，您可以执行以下操作：

df.loc[:]['A'] = 'foo'