user1802693 user1802693 - 6 months ago 848
Python Question

Pandas read_csv dtype specify all columns but one

I've a CSV file. Most of it's values I want to read as string, but I want to read a column as bool if the column with the given title exists..

Because the CSV file has a lots of columns, I don't want to specify on each column the datatype directly and give something like this:

data = read_csv('sample.csv', dtype={'A': str, 'B': str, ..., 'X': bool})


Is it possible to define the string type on each column but one and read an optional column as a bool at the same time?

My current solution is the following (but it's very unefficient and slow):

data = read_csv('sample.csv', dtype=str) # reads all column as string
if 'X' in data.columns:
l = lambda row: True if row['X'] == 'True' else False if row['X'] == 'False' else None
data['X'] = data.apply(l, axis=1)


UPDATE:
Sample CSV:

A;B;C;X
a1;b1;c1;True
a2;b2;c2;False
a3;b3;c3;True


Or the same can ba without the 'X' column (because the column is optional):

A;B;C
a1;b1;c1
a2;b2;c2
a3;b3;c3

Answer

You can first filter columns contains value X with boolean indexing and then replace:

cols = df.columns[df.columns.str.contains('X')]
df[cols] = df[cols].replace({'True': True, 'False': False})

Or if need filter column X:

cols = df.columns[df.columns == 'X']
df[cols] = df[cols].replace({'True': True, 'False': False})

Sample:

import pandas as pd

df = pd.DataFrame({'A':['a1','a2','a3'],
                   'B':['b1','b2','b3'],
                   'C':['c1','c2','c3'],
                   'X':['True','False','True']})

print (df)
    A   B   C      X
0  a1  b1  c1   True
1  a2  b2  c2  False
2  a3  b3  c3   True
print (df.dtypes)
A    object
B    object
C    object
X    object
dtype: object

cols = df.columns[df.columns.str.contains('X')]
print (cols)

Index(['X'], dtype='object')

df[cols] = df[cols].replace({'True': True, 'False': False})

print (df.dtypes)
A    object
B    object
C    object
X      bool
dtype: object
print (df)

    A   B   C      X
0  a1  b1  c1   True
1  a2  b2  c2  False
2  a3  b3  c3   True
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