Convert whole dataframe from lower case to upper case with Pandas

问题

I have a dataframe like the one displayed below:

# Create an example dataframe about a fictional army
raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks'],
            'company': ['1st', '1st', '2nd', '2nd'],
            'deaths': ['kkk', 52, '25', 616],
            'battles': [5, '42', 2, 2],
            'size': ['l', 'll', 'l', 'm']}
df = pd.DataFrame(raw_data, columns = ['regiment', 'company', 'deaths', 'battles', 'size'])

My goal is to transform every single string inside of the dataframe to upper case so that it looks like this:

Notice: all data types are objects and must not be changed; the output must contain all objects. I want to avoid to convert every single column one by one... I would like to do it generally over the whole dataframe possibly.

What I tried so far is to do this but without success

df.str.upper()

回答1:

astype() will cast each series to the dtype object (string) and then call the str() method on the converted series to get the string literally and call the function upper() on it. Note that after this, the dtype of all columns changes to object.

In [17]: df
Out[17]: 
     regiment company deaths battles size
0  Nighthawks     1st    kkk       5    l
1  Nighthawks     1st     52      42   ll
2  Nighthawks     2nd     25       2    l
3  Nighthawks     2nd    616       2    m

In [18]: df.apply(lambda x: x.astype(str).str.upper())
Out[18]: 
     regiment company deaths battles size
0  NIGHTHAWKS     1ST    KKK       5    L
1  NIGHTHAWKS     1ST     52      42   LL
2  NIGHTHAWKS     2ND     25       2    L
3  NIGHTHAWKS     2ND    616       2    M

You can later convert the 'battles' column to numeric again, using to_numeric():

In [42]: df2 = df.apply(lambda x: x.astype(str).str.upper())

In [43]: df2['battles'] = pd.to_numeric(df2['battles'])

In [44]: df2
Out[44]: 
     regiment company deaths  battles size
0  NIGHTHAWKS     1ST    KKK        5    L
1  NIGHTHAWKS     1ST     52       42   LL
2  NIGHTHAWKS     2ND     25        2    L
3  NIGHTHAWKS     2ND    616        2    M

In [45]: df2.dtypes
Out[45]: 
regiment    object
company     object
deaths      object
battles      int64
size        object
dtype: object

回答2:

this can be solved by the following applymap operation:

df = df.applymap(lambda s:s.lower() if type(s) == str else s)

回答3:

Since str only works for series, you can apply it to each column individually then concatenate:

In [6]: pd.concat([df[col].astype(str).str.upper() for col in df.columns], axis=1)
Out[6]: 
     regiment company deaths battles size
0  NIGHTHAWKS     1ST    KKK       5    L
1  NIGHTHAWKS     1ST     52      42   LL
2  NIGHTHAWKS     2ND     25       2    L
3  NIGHTHAWKS     2ND    616       2    M

Edit: performance comparison

In [10]: %timeit df.apply(lambda x: x.astype(str).str.upper())
100 loops, best of 3: 3.32 ms per loop

In [11]: %timeit pd.concat([df[col].astype(str).str.upper() for col in df.columns], axis=1)
100 loops, best of 3: 3.32 ms per loop

Both answers perform equally on a small dataframe.

In [15]: df = pd.concat(10000 * [df])

In [16]: %timeit pd.concat([df[col].astype(str).str.upper() for col in df.columns], axis=1)
10 loops, best of 3: 104 ms per loop

In [17]: %timeit df.apply(lambda x: x.astype(str).str.upper())
10 loops, best of 3: 130 ms per loop

On a large dataframe my answer is slightly faster.

回答4:

try this

df2 = df2.apply(lambda x: x.str.upper() if x.dtype == "object" else x)

回答5:

if you want to conserv de dtype use is isinstance(obj,type)

df.apply(lambda x: x.str.upper().str.strip() if isinstance(x, object) else x)

来源：https://stackoverflow.com/questions/39512002/convert-whole-dataframe-from-lower-case-to-upper-case-with-pandas

标签

python

pandas

type-conversion

uppercase

lowercase