st: How to find the sum of a variable by a group id

[Urmi Bhattacharya <ub3@indiana.edu>]

Dear Statalisters,

I have the following data set.

hhid  childid y1
1       1       1
1        2      1
1        3      0
2        1      0
2        2      0


I need to find the sum of y1 per hhid, i.e., i need to get the
following data set

hhid    sumy1
1         2
2         0

How do I get that?

I tried the following

collapse (sum) y1, by hhid
it gives me the following error:

option by incorrectly specified
r(198);
I am using Stata 11.2.

It is a simple enough thing I am sure, but I am just not able to work
it out. It would be great if someone could tell me where am i going
wrong?

Best

Urmi
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