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

Question

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

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

Answered By: EdChum

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.

Answered By: mm_

Answer 3

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

Answered By: U13-Forward

Answer 4

You can use the method assign:

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

Answered By: Mykola Zotko

Answer 5

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

Answered By: Marioanzas

Answer 6

For this to work without receiving the slice error/warning, you can do this:

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

Answered By: Cos

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