Fill a new pandas column with row numbers
PythonPandasPython Problem Overview
I have the following DataFrame data with random index values:
A B
100 0 7
203 5 4
5992 0 10
2003 9 8
20 10 5
12 6 2
I would like to add a new column 'C' with row numbers. For example:
A B C
100 0 7 0
203 5 4 1
5992 0 10 2
2003 9 8 3
20 10 5 4
12 6 2 5
Python Solutions
Solution 1 - Python
Use numpy.arange by length of DataFrame:
df['C'] = np.arange(len(df))
Or you can use DataFrame.shape, thank you @Mehmet Burak Sayıcı:
df['C'] = np.arange(df.shape[0])
print (df)
A B C
100 0 7 0
203 5 4 1
5992 0 10 2
2003 9 8 3
20 10 5 4
12 6 2 5
Solution 2 - Python
By using reset_index
df['C'] = df.reset_index().index
df
A B C
100 0 7 0
203 5 4 1
5992 0 10 2
2003 9 8 3
20 10 5 4
12 6 2 5
To generalise:
df['C'] = df.index if df.index.is_monotonic_increasing else range(len(df))
df
A B C
100 0 7 0
203 5 4 1
5992 0 10 2
2003 9 8 3
20 10 5 4
12 6 2 5
Solution 3 - Python
We can add new column with row numbers as first column as following:
import pandas as pd
import numpy as np
df = pd.DataFrame({'B': [1, 2, 3], 'C': [4, 5, 6]})
B C
0 1 4
1 2 5
2 3 6
df.insert(loc=0, column='A', value=np.arange(len(df)))
A B C
0 0 1 4
1 1 2 5
2 2 3 6
Solution 4 - Python
You don't need numpy to achieve the same as in the previous answer:
df.insert(loc=0, column="A", value=df.reset_index().index)