Nothing
# A. Multiple return statements
test1 <- function(x) {
y <- x + 1
if (x < 10) return(list(x = x, y = y))
z <- x + 2
if (x >= 10) return(list(x = x, z = z))
}
unlist(test1(x = 7)); unlist(test1(x = 15))
# B1. Use list to hold reults: define it at the end
test2 <- function(aa) {
# Body: transformation
bb <- aa + 83
if (aa > 10) {cc <- aa * 3}
# Body: output
if (aa < 10) {
result <- list(aa = aa, bb = bb) # list at the end
} else {
result <- list(aa = aa, bb = bb, cc = cc)
}
return(result)
}
unlist(test2(aa = 8)); unlist(test2(aa = 11))
# B1. Use list to hold reults: define it at the beginning
test3 <- function(aa) {
# Body: transformation and output selection
result <- list(); result$aa <- aa
bb <- aa + 83; result$bb <- bb
if (aa > 10) {result$cc <- aa * 3}
# Body: output
return(result)
}
unlist(test3(aa = 8)); unlist(test3(aa = 11))
# C1. Output: a value is returned and can be printed without saving
# The following three treatments are the same.
test4 <- function(x) {y <- x + 1; return(y)}; test4(10)
test5 <- function(x) {y <- x + 1; y}; test5(10)
test6 <- function(x) {x + 1}; test6(10)
# C2. Output: a value is returned, but cannot be printed directly
test7 <- function(x) {y <- x + 1}
test8 <- function(x) {y <- x + 1; invisible(y)}
test9 <- function(x) {y <- x + 1; invisible(list(y, x))}
test7(10); test8(10); test9(10) # No, cannot print the output
(r7 <- test7(10)); (r8 <- test8(10)); (r9 <- test9(10)) # Yes, can print
# comparison: with or without invisible()
identical(r7, r8) # TRUE
# D. Functions without returning a value
plot.default; write.table
out <- plot(1:10); out # out is NULL
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