Reorder levels of a factor without changing order of values
I have data frame with some numerical variables and some categorical factor variables. The order of levels for those factors is not the way I want them to be.
numbers <- 1:4
letters <- factor(c("a", "b", "c", "d"))
df <- data.frame(numbers, letters)
df
# numbers letters
# 1 1 a
# 2 2 b
# 3 3 c
# 4 4 d
If I change the order of the levels, the letters no longer are with their corresponding numbers (my data is total nonsense from this point on).
levels(df$letters) <- c("d", "c", "b", "a")
df
# numbers letters
# 1 1 d
# 2 2 c
# 3 3 b
# 4 4 a
I simply want to change the level order, so when plotting, the bars are shown in the desired order - which may differ from default alphabetical order.
使用factor的levels参数：
df <- data.frame(f = 1:4, g = letters[1:4])
df
# f g
# 1 1 a
# 2 2 b
# 3 3 c
# 4 4 d
levels(df$g)
# [1] "a" "b" "c" "d"
df$g <- factor(df$g, levels = letters[4:1])
# levels(df$g)
# [1] "d" "c" "b" "a"
df
# f g
# 1 1 a
# 2 2 b
# 3 3 c
# 4 4 d
some more, just for the record
## reorder is a base function
df$letters <- reorder(df$letters, new.order=letters[4:1])
library(gdata)
df$letters <- reorder.factor(df$letters, letters[4:1])
You may also find useful Relevel and combine_factor.
so what you want, in R lexicon, is to change only the labels for a given factor variable (ie, leave the data as well as the factor levels, unchanged).
df$letters = factor(df$letters, labels=c("d", "c", "b", "a"))
given that you want to change only the datapoint-to-label mapping and not the data or the factor schema (how the datapoints are binned into individual bins or factor values, it might help to know how the mapping is originally set when you initially create the factor.
the rules are simple:
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