Pasting several values from a vector into a dataframe column

Question

My dataframe "test" is like this:

a b c
d e f

I want to add strings to the 1st col so as to get this

        a__3  b c
        a__23 b c
        a__45 b c 

         ...

    sb <- c(3, 23, 45)
    datalist <- ""



       for (i in 1:length(sb)) {
       new <- apply(test[,1],1,paste0,collapse=("__" sb[i]))
        datalist[i] <- new
    }

I want to add rows into test df including all sb[i] .

I have tried rbind , but does not get the correct result

Answer 1

An idea is to replicate the rows based on the length of your sb vector, do the paste and filter to keep only the ones you are interested in, ie

d3 <- d2[rep(rownames(d2), length(sb)),]
d3$V1[d3$V1 == 'a'] <- paste0(d3$V1[d3$V1 == 'a'], '__', sb)
d3[grepl('a', d3$V1),]

#       V1 V2 V3
#1    a__3  b  c
#1.1 a__23  b  c
#1.2 a__45  b  c

DATA

dput(d2)
structure(list(V1 = c("a", "d"), V2 = c("b", "e"), V3 = c("c", 
"f")), row.names = c(NA, -2L), class = "data.frame")