I want to find the number of NaN
in each column of my data so that I can drop a column if it has fewer NaN
than some threshold. I looked but wasn't able to find any function for this. value_counts
is too slow for me because most of the values are distinct and I'm only interested in the NaN
count.
You can use the isna()
method (or it's alias isnull()
which is also compatible with older pandas versions < 0.21.0) and then sum to count the NaN values. For one column:
In [1]: s = pd.Series([1,2,3, np.nan, np.nan])
In [4]: s.isna().sum() # or s.isnull().sum() for older pandas versions
Out[4]: 2
For several columns, it also works:
In [5]: df = pd.DataFrame({'a':[1,2,np.nan], 'b':[np.nan,1,np.nan]})
In [6]: df.isna().sum()
Out[6]:
a 1
b 2
dtype: int64