Remove rows where column value type is string Pandas

Question

I have a pandas dataframe. One of my columns should only be floats. When I try to convert that column to floats, I'm alerted that there are strings in there. I'd like to delete all rows where values in this column are strings...

Answer 1

Use convert_objects with param convert_numeric=True this will coerce any non numeric values to NaN:

In [24]:

df = pd.DataFrame({'a': [0.1,0.5,'jasdh', 9.0]})
df
Out[24]:
       a
0    0.1
1    0.5
2  jasdh
3      9
In [27]:

df.convert_objects(convert_numeric=True)
Out[27]:
     a
0  0.1
1  0.5
2  NaN
3  9.0
In [29]:

You can then drop them:

df.convert_objects(convert_numeric=True).dropna()
Out[29]:
     a
0  0.1
1  0.5
3  9.0

UPDATE

Since version 0.17.0 this method is now deprecated and you need to use to_numeric unfortunately this operates on a Series rather than a whole df so the equivalent code is now:

df.apply(lambda x: pd.to_numeric(x, errors='coerce')).dropna()

Answer 2

One of my columns should only be floats. I'd like to delete all rows where values in this column are strings

You can convert your series to numeric via pd.to_numeric and then use pd.Series.notnull. Conversion to float is required as a separate step to avoid your series reverting to object dtype.

# Data from @EdChum

df = pd.DataFrame({'a': [0.1, 0.5, 'jasdh', 9.0]})

res = df[pd.to_numeric(df['a'], errors='coerce').notnull()]
res['a'] = res['a'].astype(float)

print(res)

     a
0  0.1
1  0.5
3  9.0

Answer 3

Assume your data frame is df and you wanted to ensure that all data in one of the column of your data frame is numeric in specific pandas dtype, e.g float:

df[df.columns[n]] = df[df.columns[n]].apply(pd.to_numeric, errors='coerce').fillna(0).astype(float).dropna()