Question

Dear stackoverflow experts,

I have two tables

table1<-read.table("table1.txt",header=TRUE)
table2<-read.table("table2.txt",header=TRUE)

I want to select from table 1 all of the values that match values of the first column of table 2. I have try sqldf, but I´m not sure of the syntax,

selection<-sqldf("SELECT *, column1 from table1 WHERE column1 like column2 from table2")

Any suggestion?

Answer 1

You can try the following:

 table1[sapply(table1, function(x) x %in% table2[, 1, drop=FALSE])]

---

What happens here is that the sapply statement is returning a logical list indicating which elements of table1 are in table2‘s first column. We are then using that logical vector to index table1

  # to see this more clearly, try the following line, 
  # which is what is being used to index table1
  sapply(table1, function(x) x %in% table2[, 1, drop=FALSE])