dividing a string into separate columns pandas python

Question

I have seen similar questions, but nothing that really matchs my problem. If I have a table of values such as:

value
a
b
b
c

I want to use pandas to add in columns to the table to show for example:

value a b
a 1 0 
b 0 1
c 0 0

I have tried the following:

df['a'] = 0

def string_count(indicator):
    if indicator == 'a':
        df['a'] == 1

df['a'].apply(string_count)

But this produces:

 0    None
 1    None
 2    None
 3    None

I would like to at least get to the point where the choices are hardcoded in (i.e I already know that a,b and c appear), but would even better if I could look set the column of strings and then insert a column for each unique string.

Am I approaching this the wrong way?

Stefan · Accepted Answer · 2016-01-12 16:34:05Z

1

dummies = pd.get_dummies(df.value)

   a  b  c
0  1  0  0
1  0  1  0
2  0  1  0
3  0  0  1

If you only want to display unique occurrences, you can add:

dummies.index = df.value
dummies.drop_duplicates()

       a  b  c
value         
a      1  0  0
b      0  1  0
c      0  0  1

Alternatively:

df = df.join(pd.get_dummies(df.value))

  value  a  b  c
0     a  1  0  0
1     b  0  1  0
2     b  0  1  0
3     c  0  0  1

Where you could again .drop_duplicates() to only see unique entries from the value column.

edited Jan 12, 2016 at 16:34

answered Jan 12, 2016 at 16:24

Stefan

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1 Comment

DGraham Over a year ago

How can I alter this so the columns appear with the main dataframe and not as a separate dataframe?

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