In R, in a data frame, I want to take the code number of a tree species in one column and create a new column in the data frame with recoded text name of the species like below. I can create a matrix of tree name = code number, but how do I apply this to a long and mixed column of just numerical values?
> treeco <- c(4, 3, 4, 5, 3, 2, 2, 1, 4)
> spcode <- c("oak" = 1, "ash" = 2, "elm" = 3, "beech" = 4, "hazel" = 5)
> treesp <- data.frame(spcode)
> treesp
species
oak 1
ash 2
elm 3
beech 4
hazel 5
This is the solution I am looking for:
treeco spcode
1 4 beech
2 3 elm
3 4 beech
4 5 hazel
5 3 elm
6 2 ash
7 2 ash
8 1 oak
9 4 beech
data.frame(treeco, answer = names(spcode)[treeco])
# treeco answer
# 1 4 beech
# 2 3 elm
# 3 4 beech
# 4 5 hazel
# 5 3 elm
# 6 2 ash
# 7 2 ash
# 8 1 oak
# 9 4 beech
It can be slightly confusing when a column-name matches one in the environment, so for the sake of demonstration I'll rename treeco in the tibble so that it is clear which is being used.
library(dplyr)
tibble(tc = treeco) %>%
mutate(answer = names(spcode)[tc])
# # A tibble: 9 x 2
# tc answer
# <dbl> <chr>
# 1 4 beech
# 2 3 elm
# 3 4 beech
# 4 5 hazel
# 5 3 elm
# 6 2 ash
# 7 2 ash
# 8 1 oak
# 9 4 beech
There's another method that allows you to bring in much more than one extra column: the join/merge.
treecodes <- data.frame(code = spcode, tree = names(spcode))
set.seed(42)
treecodes$rand <- sample(100, size = nrow(treecodes), replace = TRUE)
treecodes
# code tree rand
# oak 1 oak 49
# ash 2 ash 65
# elm 3 elm 25
# beech 4 beech 74
# hazel 5 hazel 100
trees <- data.frame(code = treeco)
trees
# code
# 1 4
# 2 3
# 3 4
# 4 5
# 5 3
# 6 2
# 7 2
# 8 1
# 9 4
trees %>%
left_join(treecodes, by = "code")
# code tree rand
# 1 4 beech 74
# 2 3 elm 25
# 3 4 beech 74
# 4 5 hazel 100
# 5 3 elm 25
# 6 2 ash 65
# 7 2 ash 65
# 8 1 oak 49
# 9 4 beech 74
For more information on joins/merges, see How to join (merge) data frames (inner, outer, left, right) and What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?.