CODEWITHSUNDEEP
pythonpandasdataframe
Beto
Beto

Reputation: 579

How to check null value in rows of a column of a dataframe?

I am wanting to replace the null values with the year value. Given the following dataframe:

year value
2000  1
NaN   2
NaN   3     
NaN   4
NaN   5
NaN   6  
2001  1
NaN   2
NaN   3     
NaN   4
NaN   5
NaN   6  
...
2020  1
NaN   2
NaN   3     
NaN   4
NaN   5
NaN   6

The null values between the years, for example 2000 and 2001, I would like to substitute for 2000 until arriving in 2001 and so on. It should look something like this:

year value
2000   1
2000   2
2000   3     
2000   4
2000   5
2000   6
2001   1
2001   2
2001   3     
2001   4
2001   5
2001   6  
...
2020   1
2020   2
2020   3     
2020   4
2020   5
2020   6

I tried to do this:

size = df["year"].size
val = df.iloc[0,0]
for i in range(size):
    if df.iloc[i,0]==None:
        df.iloc[i,0]=val
    else:
        val = df.iloc[i,0]

But the dataframe remains the same. Apparently the condition if df.iloc [i, 0] == None does not work. In this sense, how to check if a column element is null?

Upvotes: 0

Views: 334

Answers (1)

Mayank Porwal
Mayank Porwal

Reputation: 34066

Use df.ffill():

In [1067]: df.year = df.year.ffill()

In [1068]: df
Out[1068]: 
      year  value
0   2000.0      1
1   2000.0      2
2   2000.0      3
3   2000.0      4
4   2000.0      5
5   2000.0      6
6   2001.0      1
7   2001.0      2
8   2001.0      3
9   2001.0      4
10  2001.0      5
11  2001.0      6

Upvotes: 1

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