R paste0 2 columns if not NA -

i paste0 2 columns if element in 1 column not na.if 1 element
of 1 columns na keep element of other column only.

structure(list(col1 = structure(1:3, .label = c("a", "b", "c"),            class = "factor"), col2 = c(1, na, 3)), .names = c("col1", "col2"),            class =   "data.frame",row.names = c(na, -3l))  #   col1 col2 # 1       1 # 2    b   na # 3    c    3  structure(list(col1 = structure(1:3, .label = c("a", "b", "c"),           class = "factor"),col2 = c(1, na, 3), col3 = c("a|1", "b", "c|3")),          .names = c("col1", "col2", "col3"), row.names = c(na,-3l),           class = "data.frame")  #  col1 col2 col3 #1       1  a|1 #2    b   na    b #3    c    3  c|3 

as @roland says, easy using ifelse (just translate mental logic series of nested ifelse statements):

x <- transform(x,col3=ifelse(is.na(col1),as.character(col2),                      ifelse(is.na(col2),as.character(col1),                           paste0(col1,"|",col2)))) 

update: need as.character in cases.