Finding intersection of dataframe rownames

Question

I have two dataframes. The row names in both are dates. What I want to do is, I want to select all the common rows (having same dates) in both the data frames and create a new data frame having only these common rows.

Of course the individual columns would get appended next to each other.

Can anyone please help??

Downvoting a new user and no constructive feedback? *sigh* – Ricardo Saporta Mar 18 '13 at 22:25 — Ricardo Saporta, Mar 18 '13 at 22:25
@RicardoSaporta Agreed, shame on them. – Brandon Bertelsen May 27 '15 at 01:39 — Brandon Bertelsen, May 27 '15 at 01:39

score 5 · Answer 1 · edited Mar 18 '13 at 22:24

5

Try:

merge(df1, df2, by="row.names")
?merge

Can also use by=0 instead of 'row.names'. And BTW the rownames are not R Date class, but are character valued. I suppose one could also do this:

 cbind( df1[ intersect(rownames(df1), rownames(df2)), ] ,
        df2[ intersect(rownames(df1), rownames(df2)), ] )

edited Mar 18 '13 at 22:24

thelatemail

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answered Mar 18 '13 at 21:55

IRTFM

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that old +1 and delete my half typed response. – mnel Mar 18 '13 at 21:56
I did take time to check ?merge. Should have given you time to finish. – IRTFM Mar 18 '13 at 21:58
1

I was writing a paragraph on the terminology of inner and outer joins. – mnel Mar 18 '13 at 22:00
Well, this is an inner join. If you want an outer join, use all=TRUE. Also note that any duplicates in either set will create n^2 tuples within that value. – IRTFM Mar 18 '13 at 22:01
that was the gist of my paragraph, yes. – mnel Mar 18 '13 at 22:04

score 0 · Answer 2 · answered May 27 '15 at 01:20

Based on BondedDust's Answer's, if you use the first line of his suggestion you can get the data like you want, since you will define an intersection of the data with the function "intersect",filter the data with the operators ('[' and ']') and bind the data by columns with the 'cbind' function.

cbind( df1[ intersect(rownames(df1), rownames(df2)), ])

Finding intersection of dataframe rownames

2 Answers2