Add values to new column from a dict with keys matching the index of a dataframe

I have a dictionary that for examples sake, looks like

{'a': 1, 'b': 4, 'c': 7}

I have a dataframe that has the same index values as the keys in this dict.

I want to add each value from the dict to the dataframe.

I feel like doing a check for every row of the DF, checking the index value, matching it to the one in the dict, then trying to add it is going to be a very slow way right?

Answer

You can use map and assign back to a new column:

d = {'a': 1, 'b': 4, 'c': 7}
df = pd.DataFrame({'c':[1,2,3]},index=['a','b','c'])

df['new_col'] = df.index.map(d)

prints:

   c  new_col
a  1        1
b  2        4
c  3        7