Reorder rows using custom order
RDplyrR Problem Overview
Given data:
library(data.table)
DT = data.table(category=LETTERS[1:3], b=1:3)
DT
# category b
# 1: A 1
# 2: B 2
# 3: C 3
Using dplyr
, how to rearrange rows to get specific order c("C", "A", "B")
in category
?
# category b
# 1: C 3
# 2: A 1
# 3: B 2
R Solutions
Solution 1 - R
First, create a vector with the letters in the desired order. Then match
* the vector with the variable to be sorted. match
returns indices of (first) matches, which can be plugged into slice
:
library(dplyr)
# create a vector with letters in the desired order
x <- c("C", "A", "B")
DT %>%
slice(match(x, category))
# category b
# 1 C 3
# 2 A 1
# 3 B 2
Another way would be to convert "category" to a factor
, set levels
to the desired order, and use arrange
:
DT %>%
mutate(category = factor(category, levels = x)) %>%
arrange(category)
# category b
# 1 C 3
# 2 A 1
# 3 B 2
*The match
method is inspired by this answer.
Solution 2 - R
An alternative could be the following, note that arrange can take a list of new indices.
library(dplyr)
df <- data.frame(category = LETTERS[1:3], b = 1:3, stringsAsFactors = F)
# create a vector with letters in the desired order
x <- c("C", "A", "B")
df %>%
arrange(sapply(category, function(y) which(y == x))