Adding column to dataframe based on another dataframe using pandas

Question

I need to create a new column in dataframe based on intervals from another dataframe. For example, I have a dataframe where in the time column I have values ​​and I want to create column in another dataframe based on the intervals in that time column.

I think a practical example is simpler to understand:

Dataframe with intervals

df1

    time    value   var2
0   1.0     34.0    35.0
1   4.0     754.0   755.0
2   9.0     768.0   769.0
3   12.0    65.0    66.0

Dataframe that I need to filter

df2

    time   value    var2
0   1.0    23.0     23.0 
1   2.0    43.0     43.0   
2   3.0    76.0     12.0 
3   4.0    88.0     22.0 
4   5.0    64.0     45.0 
5   6.0    98.0     33.0 
6   7.0    76.0     11.0 
7   8.0    56.0     44.0 
8   9.0    23.0     22.0 
9   10.0   54.0     44.0 
10  11.0   65.0     22.0 
11  12.0   25.0     25.0 

should result

df3

    time   value    var2    interval
0   1.0    23.0     23.0     1
1   2.0    43.0     43.0     1  
2   3.0    76.0     12.0     1
3   4.0    88.0     22.0     1
4   5.0    64.0     45.0     2
5   6.0    98.0     33.0     2
6   7.0    76.0     11.0     2
7   8.0    56.0     44.0     2
8   9.0    23.0     22.0     2
9   10.0   54.0     44.0     3
10  11.0   65.0     22.0     3
11  12.0   25.0     25.0     3

EDIT: As Shubham Sharma said, it's not a filter, I want to add a new column based on intervals in other dataframe.

Answer 1

You can use pd.cut to categorize the time in df2 into discrete intervals based on the time in df1 then use Series.factorize to obtain a numeric array identifying distinct ordered values.

df2['interval'] = pd.cut(df2['time'], df1['time'], include_lowest=True)\
                    .factorize(sort=True)[0] + 1

Result:

    time  value  var2  interval
0    1.0   23.0  23.0         1
1    2.0   43.0  43.0         1
2    3.0   76.0  12.0         1
3    4.0   88.0  22.0         1
4    5.0   64.0  45.0         2
5    6.0   98.0  33.0         2
6    7.0   76.0  11.0         2
7    8.0   56.0  44.0         2
8    9.0   23.0  22.0         2
9   10.0   54.0  44.0         3
10  11.0   65.0  22.0         3
11  12.0   25.0  25.0         3