Fill in data frame with values from rows above

Question

Say I have a data frame like this:

ID,  ID_2, FIRST, VALUE
-----------------------
\'a\', \'aa\', TRUE, 2
\'a\', \'ab\', FALSE, NA
\'a\', \'ac\', FALSE, NA
\         


        

Answer 1

+1 for @nacnudus Handles leading blanks

f4 <- function(x, blank = is.na) {

  # Find the values
  if (is.function(blank)) {
    isnotblank <- !blank(x)
  } else {
    isnotblank <- x != blank
  }

  # Fill down
  xfill <- cumsum(isnotblank) 
  xfill[ xfill == 0 ] <- NA

  # Replace Blanks
  xnew <- x[ which(isnotblank) ][ xfill ]
  xnew[is.na(xnew)] <- blank
  return(xnew)
}