Iterate and input data into a column in a pandas dataframe

Question

I have a pandas dataframe with a column that is a small selection of strings. Let's call the column 'A' and all of the values in it are string_1, string_2, string_3.

Now, I want to add another column and fill it with numeric values that correspond to the strings.

I created a dictionary

d = { 'string_1' : 1, 'string_2' : 2, 'string_3': 3}

I then initialized the new column:

df['B'] = pd.Series(index=df.index)

Now, I want to fill it with the integer values. I can call the values associated with the strings in the dictionary by:

for s in df['A']:
   n = d[s]

That works fine, but I've tried using just plain df['B'] = n to fill the new column in the for-loop, but that doesn't work, and I've tried to figure out indexing with pandas.

EdChum · Accepted Answer · 2014-06-14 22:42:46Z

1

If I understand you correctly you can just call map:

df['B'] = df['A'].map(d)

This will perform the lookup and fill the values you are looking for.

answered Jun 14, 2014 at 22:42

EdChum

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Andy Hayden · Accepted Answer · 2014-06-14 22:43:02Z

0

Rather than fill as an empty column, you can simply populate this with an apply:

df['B'] = df['A'].apply(d.get)

answered Jun 14, 2014 at 22:43

Andy Hayden

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