reorder a numeric column based on levels of another column-CodePudding

I would like to reorder my numeric column according to the factor levels of group column. my toy data looks as following:

toy.df  <- data.frame(group = c(rep("C",3), rep("B", 2),rep("A", 1)), num = c(rep(10, 3), rep(5,2), 20))
toy.df$group <- factor(toy.df$group, levels = c('B', 'A', 'C'))
toy.df$num <- factor(toy.df$num, levels = c('B', 'A', 'C'))

The last line of code is not working. Do you have any idea how I can set the levels of column num using levels of column group.

thanks

CodePudding user response：

Assuming you want to level order of num to mirror the level order of group, such that the levels of num are 5, 20, 10 then you could sort your data frame by group and then use forcats::fct_inorder. This will assign the factor levels of num in order of appearance:

library(tidyverse)

df <- toy.df %>% 
  arrange(group) %>% 
  mutate(num = fct_inorder(factor(num)))

levels(df$num)
[1] "5"  "20" "10"

Note: this will change the order of your data frame.

You can also use fct_reorder using a custom function to reorder num that's based on group:

df <- toy.df %>% 
  mutate(num = fct_reorder(factor(num), group, function(x) as.numeric(unique(x))))

Alternatively, you could sort the data and then pull out the unique values of num which are ordered by group and use that to assign the levels:

df <- toy.df %>% 
  mutate(num = factor(num, unique(arrange(toy.df, group)$num)))