count unique values in one column for specific values in another column,

Question

I have a data frame on bills that has (among other variables) a column for 'year', a column for 'issue', and a column for 'sub issue.' A simplified example df looks like this:

year   issue   sub issue 
1970   4       20
1970   3       21
1970   4       22
1970   2       8
1971   5       31
1971   4       22
1971   9       10
1971   3       21
1971   4       22

Etc., for about 60 years. I want to count the unique values in the issue and sub issue columns for each year, and use those to create a new df- dat2. Using the df above, dat2 would look like this:

year   issues    sub issues
1970    3        4
1971    4        4

Weary of factors, I confirmed that the values in all columns are integers, if that makes a difference. I am new at R (obviously), and I haven't been able to find relevant code for this specific purpose online. Thanks for any help!!

Jealie · Accepted Answer · 2014-03-06 00:50:04Z

7

That's a one-liner, with aggregate:

with(d,aggregate(cbind(issue,subissue) ~ year,FUN=function(x){length(unique(x))}))

returning:

  year issue subissue
1 1970     3        4
2 1971     4        4

answered Mar 6, 2014 at 0:50

Jealie

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