Pandas: How to create a column based on values of another column?

问题

I need to create a new column at the end of a data frame, where the values in that new column are the result of applying some function who's parameters are based on other columns. Specifically, from another column, but a different row. So for example, if my data frame had two columns, containing values x_i, y_i respectively, my third column would be f(x_(i-1), y_(i-1))

I know that to create create a new column, the easiest way would be to do something like

df['new_row'] = ...

But I'm not sure what I can set to that.

How do I do this?

回答1:

Something like this? Or is your function more complicated?

print(df)

   0  1  2  3
0  1  2  3  4

df[4]= df[2]*df[3]/.3

print(df)

   0  1  2  3   4
0  1  2  3  4  40

回答2:

Here's an example:

df['new_col'] = df['old_col'] * df['old_col']

Or if you wrote a custom function that took in two arrays, such as:

def f(arr1, arr2):
        new_arr = # put logic here
        return newer

You could try:

df['new_col'] = f(df['old_col'], df['old_col2'])

回答3:

1   3
3   3
43  4
2   3

with open("file", 'r') as f:
     for line in f:
        n, r = line.split()
        formula = pow(int(n),int(r))
        print("{:4}{:4}{:9}".format(n,r, formula))

output

1    3           1

3    3          27

43  4     3418801

2   3           8

来源：https://stackoverflow.com/questions/32752087/pandas-how-to-create-a-column-based-on-values-of-another-column