Add row counts to entire dataframe

Question

I'm getting row counts for a particular column like so:

subreddit_count = df['body'].groupby(df['subreddit']).agg(['count'])

Which returns the following df:

subreddit   count
0   0xProject   12
1   100sexiest  1
2   100yearsago 2
3   1022    3
4   1200isjerky 2
5   1200isplenty    37
6   1200isplentyketo    1
7   12ozmouse   1
8   12thMan 4
9   12winArenaLog   1
10  13ReasonsWhy    5
11  13or30  3
12  14ers   1
13  1500isplenty    1
14  15SecondStories 3
15  18650masterrace 1
16  18_19   10
17  1911    5
18  195 2
19  19KidsandCounting   4
20  1P_LSD  18
21  2007oneclan 2
22  2007scape   1044
23  2010sMusic  1
24  21savage    1
25  22lr    1
26  23andme 9
27  240sx   4
28  24CarrotCraft   1
29  24hoursupport   5

I would like to essentially undo the groupby so that these counts are added to every row in the original df. I've tried using reset_index to no avail. What's the right approach here?