merge only one column in r code example

Example 1: r merge by two columns

x <- data.frame(k1=c(NA,NA,3,4,5), k2=c(1,NA,NA,4,5), data=1:5)
y <- data.frame(k1=c(NA,2,NA,4,5), k2=c(NA,NA,3,4,5), data=1:5)
merge(x, y, by=c("k1","k2"))

Example 2: how to combine all columns into one column in r

unite(data, col, ..., sep = "_", remove = TRUE, na.rm = FALSE)