x <- c("female", "f", "male", "m", "f", "undeclared")
y <- factor(x)
y
# [1] female f male m f undeclared
# Levels: f female m male undeclared
levels(y) <- list("female" = c("female", "f"),
"male" = c("male", "m"),
"undeclared" = "undeclared")
y
# [1] female female male male female undeclared
# Levels: female male undeclared