Leave only those rows in matrices which have equal elements at certain column

Question

Let me show an example. Consider we have 3 tables (focus on columns N):

   Table 1         Table 2        Table 3
-------------   -------------   -------------
           


        

Answer 1

Use a set intersection to find the common values of N amongst all the tables

> t1 <-data.frame(N=c(5,10,15),Values=c(1,2,3))
> t2 <-data.frame(N=c(5,6,10,15),Values=c(-1,-2,-3,-4))
> t3 <-data.frame(N=c(5,6,10,12,15),Values=c(1,21,5,6,3))
> common<-intersect(intersect(t1$N,t2$N),t3$N)
> common
[1]  5 10 15

Then just subset each table to find the rows with those common values

> newt1<-t1[t1$N %in% common,]
> newt2<-t2[t2$N %in% common,]
> newt3<-t3[t3$N %in% common,]
> newt3
   N Values
1  5      1
3 10      5
5 15      3

This approach should scale such that you can create a function and pass in a vector of data frames and a column name. It can return a vector of new data frames.

I've used data frames. The same approach will work with matrices