Python pandas: output dataframe to csv with integers

Question

I have a pandas.DataFrame that I wish to export to a CSV file. However, pandas seems to write some of the values as float instead of int

Answer 1

The problem is that since you are assigning things by rows, but dtypes are grouped by columns, so things get cast to object dtype, which is not a good thing, you lose all efficiency. So one way is to convert which will coerce to float/int dtype as needed.

As we answered in another question, if you construct the frame all at once (or construct column by column) this step will not be needed

In [23]: def convert(x):
   ....:     try:
   ....:         return x.astype(int)
   ....:     except:
   ....:         return x
   ....:     

In [24]: df.apply(convert)
Out[24]: 
    a   b   c   d
x  10  10 NaN  10
y   1   5   2   3
z   1   2   3   4

In [25]: df.apply(convert).dtypes
Out[25]: 
a      int64
b      int64
c    float64
d      int64
dtype: object

In [26]: df.apply(convert).to_csv('test.csv')

In [27]: !cat test.csv
,a,b,c,d
x,10,10,,10
y,1,5,2.0,3
z,1,2,3.0,4