如何从整个数据框中删除所有非数字数字：调试

Question

I am attempting to remove all non-numeric characters from my dataframe (ie characters like ]$^M# etc.) with a single line of code. The data frame is a Google Play Store apps dataset.

df = pd.read_csv("googleplaystore.csv")

df['Rating'].fillna(value = '0.0', inplace = True)

#sample data#

   Rating    Reviews                Size     Installs  Type Price  \
0        4.1     159                 19M      10,000+  Free     0   
1        3.9     967                 14M     500,000+  Free     0   
2        4.7   87510                8.7M   5,000,000+  Free     0   
3        4.5  215644                 25M  50,000,000+  Free     0   
4        4.3     967                2.8M     100,000+  Free     0   
...      ...     ...                 ...          ...   ...   ...   
10836    4.5      38                 53M       5,000+  Free     0   
10837      5       4                3.6M         100+  Free     0   
10838    0.0       3                9.5M       1,000+  Free     0   
10839    4.5     114  Varies with device       1,000+  Free     0   
10840    4.5  398307                 19M  10,000,000+  Free     0   


Content Rating                     Genres      Last Updated  \
0           Everyone               Art & Design   January 7, 2018   
1           Everyone  Art & Design;Pretend Play  January 15, 2018   
2           Everyone               Art & Design    August 1, 2018   
3               Teen               Art & Design      June 8, 2018   
4           Everyone    Art & Design;Creativity     June 20, 2018   
...              ...                        ...               ...   
10836       Everyone                  Education     July 25, 2017   
10837       Everyone                  Education      July 6, 2018   
10838       Everyone                    Medical  January 20, 2017   
10839     Mature 17+          Books & Reference  January 19, 2015   
10840       Everyone                  Lifestyle     July 25, 2018

clean_data = df.replace('[^\d.]', '', regex = True).astype(float)

Essentially I am trying to remove the 'M' from the Size column after the digits as well as the '+' sign in the Installs column.

But I'm returned with this error message;

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-325-887d47a9889e> in <module>
----> 1 data_ = df.replace('[^\d.]', '', regex = True).astype(float)

~\anaconda3\lib\site-packages\pandas\core\generic.py in astype(self, dtype, copy, errors)
   5696         else:
   5697             # else, only a single dtype is given
-> 5698             new_data = self._data.astype(dtype=dtype, copy=copy, errors=errors)
   5699             return self._constructor(new_data).__finalize__(self)
   5700 

~\anaconda3\lib\site-packages\pandas\core\internals\managers.py in astype(self, dtype, copy, errors)
    580 
    581     def astype(self, dtype, copy: bool = False, errors: str = "raise"):
--> 582         return self.apply("astype", dtype=dtype, copy=copy, errors=errors)
    583 
    584     def convert(self, **kwargs):

~\anaconda3\lib\site-packages\pandas\core\internals\managers.py in apply(self, f, filter, **kwargs)
    440                 applied = b.apply(f, **kwargs)
    441             else:
--> 442                 applied = getattr(b, f)(**kwargs)
    443             result_blocks = _extend_blocks(applied, result_blocks)
    444 

~\anaconda3\lib\site-packages\pandas\core\internals\blocks.py in astype(self, dtype, copy, errors)
    623             vals1d = values.ravel()
    624             try:
--> 625                 values = astype_nansafe(vals1d, dtype, copy=True)
    626             except (ValueError, TypeError):
    627                 # e.g. astype_nansafe can fail on object-dtype of strings

~\anaconda3\lib\site-packages\pandas\core\dtypes\cast.py in astype_nansafe(arr, dtype, copy, skipna)
    895     if copy or is_object_dtype(arr) or is_object_dtype(dtype):
    896         # Explicit copy, or required since NumPy can't view from / to object.
--> 897         return arr.astype(dtype, copy=True)
    898 
    899     return arr.view(dtype)

ValueError: could not convert string to float: 

Kindly assist in debugging if possible. I would really like to keep it to one line of code for the entire data frame. Thank you in advance.

Answer 1

I think problem is need specify columns for replace and replace empty value to NaN or 0 if not numeric like second last Size value:

cols = ['Size','Installs']
df[cols] = df[cols].replace('[^\d.]', '', regex = True).replace('',np.nan).astype(float)

print (df)
       Rating  Reviews  Size    Installs  Type  Price
0         4.1      159  19.0     10000.0  Free      0
1         3.9      967  14.0    500000.0  Free      0
2         4.7    87510   8.7   5000000.0  Free      0
3         4.5   215644  25.0  50000000.0  Free      0
4         4.3      967   2.8    100000.0  Free      0
10836     4.5       38  53.0      5000.0  Free      0
10837     5.0        4   3.6       100.0  Free      0
10838     0.0        3   9.5      1000.0  Free      0
10839     4.5      114   NaN      1000.0  Free      0
10840     4.5   398307  19.0  10000000.0  Free      0

Answer 2

The problem is that you are replacing all non-numeric characters in your dataframe with "".

This means that a non-numeric string ends up as "" - a zero-length string. That can't be interpreted as a float, so you get the error.

If you run the replace over just your rating column

df["Rating"].replace('[^\d.]', '', regex = True).astype(float)

then it works, because removing non-numeric characters from that column results in a column filled only with characters that can be converted into numbers.

However, running it over the whole dataframe doesn't work because so many of your values are purely non-numeric. The genre column, for example, will end up as just a column of empty strings, throwing the error.