Iterating over a list of strings for operations in Python

Question

I'm trying to do a rather simple loop in Python 3.6.1 that involves a list of strings. Essentially, I have a dataframe that looks like this:

      X_out  Y_out  Z_in  X_in  Y_in  Z_in      
Year                                                                
1969    4     3     4      4     3     3
1970    2     0     1      3     2     2
1971    3     1     1      0     1     2
1972    2     0     0      3     1     0

and I'd like to find the net change of X, Y, and Z, making them new columns in this dataframe.

In its simplest form, this could be

df['x_net'] = df['x_in'] - df['x_out']
df['y_net'] = df['y_in'] - df['y_out']
df['z_net'] = df['z_in'] - df['z_out']

but in actuality, there are about fifteen columns that need to be created in this way. Since it'll be a bear, I figure it's best to put in a function, or at least a loop. I made a list of our initial "root" variables, without the suffixes that looks like this:

root_vars = ['x', 'y', 'z']

And I think that my code might(?) look something like:

for i in root_vars:
    df['%s_net'] = df['%s_in'] - df['%s_out'] %(root_vars_[i])

but that's definitely not right. Could someone give me a hand on this one please?

Thank you so much!

glibdud · Accepted Answer · 2018-01-18 15:00:02Z

1

You can use the relatively new (Python 3.6) formatted string literals:

for i in root_vars:
    df[f'{i}_net'] = df[f'{i}_in'] - df[f'{i}_out']

The f prefix before each string causes the {i} to be replaced with the value of the variable i. If you want the code to be usable in Python versions before 3.6, you can go with the more usual formatting:

for i in root_vars:
    df['{}_net'.format(i)] = df['{}_in'.format(i)] - df['{}_out'.format(i)]

edited Jan 18, 2018 at 15:00

answered Jan 18, 2018 at 14:51

glibdud

7,9704 gold badges32 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Maia Over a year ago

It worked! Thank you so much, I really appreciate it!

Collectives™ on Stack Overflow

Iterating over a list of strings for operations in Python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related