Selecting Pandas Columns by dtype

Question

I was wondering if there is an elegant and shorthand way in Pandas DataFrames to select columns by data type (dtype). i.e. Select only int64 columns from a DataFrame.

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Answer 1

df.select_dtypes(include=[np.float64])

Answer 2

df.loc[:, df.dtypes == np.float64]

Answer 3

I'd like to extend existing answer by adding options for selecting all floating dtypes or all integer dtypes:

Demo:

np.random.seed(1234)

df = pd.DataFrame({
        'a':np.random.rand(3), 
        'b':np.random.rand(3).astype('float32'), 
        'c':np.random.randint(10,size=(3)).astype('int16'),
        'd':np.arange(3).astype('int32'), 
        'e':np.random.randint(10**7,size=(3)).astype('int64'),
        'f':np.random.choice([True, False], 3),
        'g':pd.date_range('2000-01-01', periods=3)
     })

yields:

In [2]: df
Out[2]:
          a         b  c  d        e      f          g
0  0.191519  0.785359  6  0  7578569  False 2000-01-01
1  0.622109  0.779976  8  1  7981439   True 2000-01-02
2  0.437728  0.272593  0  2  2558462   True 2000-01-03

In [3]: df.dtypes
Out[3]:
a           float64
b           float32
c             int16
d             int32
e             int64
f              bool
g    datetime64[ns]
dtype: object

Selecting all floating number columns:

In [4]: df.select_dtypes(include=['floating'])
Out[4]:
          a         b
0  0.191519  0.785359
1  0.622109  0.779976
2  0.437728  0.272593

In [5]: df.select_dtypes(include=['floating']).dtypes
Out[5]:
a    float64
b    float32
dtype: object

Selecting all integer number columns:

In [6]: df.select_dtypes(include=['integer'])
Out[6]:
   c  d        e
0  6  0  7578569
1  8  1  7981439
2  0  2  2558462

In [7]: df.select_dtypes(include=['integer']).dtypes
Out[7]:
c    int16
d    int32
e    int64
dtype: object

Selecting all numeric columns:

In [8]: df.select_dtypes(include=['number'])
Out[8]:
          a         b  c  d        e
0  0.191519  0.785359  6  0  7578569
1  0.622109  0.779976  8  1  7981439
2  0.437728  0.272593  0  2  2558462

In [9]: df.select_dtypes(include=['number']).dtypes
Out[9]:
a    float64
b    float32
c      int16
d      int32
e      int64
dtype: object

Answer 4

Optionally if you don't want to create a subset of the dataframe during the process, you can directly iterate through the column datatype.

I haven't benchmarked the code below, assume it will be faster if you work on very large dataset.

[col for col in df.columns.tolist() if df[col].dtype not in ['object','<M8[ns]']] 

Answer 5

If you want to select int64 columns and then update "in place", you can use:

int64_cols = [col for col in df.columns if is_int64_dtype(df[col].dtype)]
df[int64_cols]

For example, notice that I update all the int64 columns in df to zero below:

In [1]:

    import pandas as pd
    from pandas.api.types import is_int64_dtype

    df = pd.DataFrame({'a': [1, 2] * 3,
                       'b': [True, False] * 3,
                       'c': [1.0, 2.0] * 3,
                       'd': ['red','blue'] * 3,
                       'e': pd.Series(['red','blue'] * 3, dtype="category"),
                       'f': pd.Series([1, 2] * 3, dtype="int64")})

    int64_cols = [col for col in df.columns if is_int64_dtype(df[col].dtype)] 
    print('int64 Cols: ',int64_cols)

    print(df[int64_cols])

    df[int64_cols] = 0

    print(df[int64_cols]) 

Out [1]:

    int64 Cols:  ['a', 'f']

           a  f
        0  1  1
        1  2  2
        2  1  1
        3  2  2
        4  1  1
        5  2  2
           a  f
        0  0  0
        1  0  0
        2  0  0
        3  0  0
        4  0  0
        5  0  0

Just for completeness:

df.loc() and df.select_dtypes() are going to give a copy of a slice from the dataframe. This means that if you try to update values from df.select_dtypes(), you will get a SettingWithCopyWarning and no updates will happen to df in place.

For example, notice when I try to update df using .loc() or .select_dtypes() to select columns, nothing happens:

In [2]:

    df = pd.DataFrame({'a': [1, 2] * 3,
                       'b': [True, False] * 3,
                       'c': [1.0, 2.0] * 3,
                       'd': ['red','blue'] * 3,
                       'e': pd.Series(['red','blue'] * 3, dtype="category"),
                       'f': pd.Series([1, 2] * 3, dtype="int64")})

    df_bool = df.select_dtypes(include='bool')
    df_bool.b[0] = False

    print(df_bool.b[0])
    print(df.b[0])

    df.loc[:, df.dtypes == np.int64].a[0]=7
    print(df.a[0])

Out [2]:

    False
    True
    1

Answer 6

Since 0.14.1 there's a select_dtypes method so you can do this more elegantly/generally.

In [11]: df = pd.DataFrame([[1, 2.2, 'three']], columns=['A', 'B', 'C'])

In [12]: df.select_dtypes(include=['int'])
Out[12]:
   A
0  1

To select all numeric types use the numpy dtype numpy.number

In [13]: df.select_dtypes(include=[np.number])
Out[13]:
   A    B
0  1  2.2

In [14]: df.select_dtypes(exclude=[object])
Out[14]:
   A    B
0  1  2.2