How do I append a repeating list to a dataframe?-CodePudding

I have a list sub = ["A","B","C","D","E","F"] and a dataframe of the following format:

I need to write a code for my dataframe to finally look like the following format:

CodePudding user response：

You can use numpy.tile and repeat elements base len(df) and len(sub) then use pandas.assign for creating dataframe.

import numpy as np
sub = ["A","B","C","D","E","F"]
sub = np.asarray(sub)

# If len(df)/len(sub)) is an integer number
df = df.assign(sub = np.tile(sub, int(len(df)/len(sub))))

# If len(df) not divide by len(sub) and have reminder
df = df.assign(sub = np.tile(sub, len(df))[:len(df)])

Check:

df = pd.DataFrame(
    {
        "col1": np.random.randint(0, 10, size=(13,)),
        "col2": np.random.randint(100, 1000, size=(13,)),
    }
)
print(df)

Output:

    col1    col2    sub
0   4        608    A
1   7        432    B
2   1        978    C
3   8        155    D
4   8        863    E
5   7        589    F
6   5        649    A
7   0        726    B
8   7        269    C
9   6        792    D
10  9        437    E
11  0        989    F
12  0        854    A

CodePudding user response：

You can create a cycle using itertools.cycle, and cut it to the appropriate length using itertools.islice.

>>> from itertools import cycle, islice
...
... cycle_list = ["A", "B", "C", "D", "E", "F"]
...
... list(islice(cycle(cycle_list), 13))

['A', 'B', 'C', 'D', 'E', 'F', 'A', 'B', 'C', 'D', 'E', 'F', 'A']

So, in your case, you can just cut it to the length of the dataframe and assign it as a new column:

import pandas as pd
import numpy as np

df = pd.DataFrame(
    {
        "col1": np.random.randint(0, 10, size=(13,)),
        "col2": np.random.randint(100, 1000, size=(13,)),
    }
)

df["col3"] = list(islice(cycle(cycle_list), len(df)))

which gives:

    col1  col2 col3
0      8   413    A
1      1   590    B
2      8   508    C
3      3   147    D
4      1   821    E
5      5   757    F
6      2   857    A
7      5   644    B
8      4   536    C
9      9   959    D
10     0   769    E
11     0   943    F
12     7   276    A