How to sort part of a data frame by multiple columns in R?

Question

Sorting has been discussed quite a bit here, but I have a particular problem. I have a data frame (df) with several columns. All the observations belong to one of three types, say C1, C2, and C3. Of the various columns, one contains a value which I will call frequency (f). Example df:

 Type freq Val 
 C3. 0.34. 10-A
 C1. 0.90. 4-A
 C2. 0.40. 5-B
 C1. 0.65. 3-C
 C2. 0.77. 5-D
 C3. 0.11. 5-D

I need to sort this table so that the primary key is the Type, and secondary key is the frequency. However, and here’s my problem, they need to be sorted by a particular order of type. I need them by C1, C3, C2. So the final table looks like this:

 Type freq Val
 C1. 0.90. 4-A
 C1. 0.65. 3-C
 C3. 0.34. 10-A
 C3. 0.11. 5-D
 C2. 0.77. 5-D
 C2. 0.40. 5-B

Is there a way to do this? To pick the particular ordering scheme of the column Type. Any suggestion is much appreciated. Thanks

Answer 1

We can convert the 'Type' to factor with levels specified in the custom order

library(dplyr)
df1 %>% 
 arrange(factor(Type, levels = c('C1.', 'C3.', 'C2.')), desc(freq))
# Type freq Val
#1 C1. 0.90. 4-A
#2 C1. 0.65. 3-C
#3 C3. 0.34. 10-A
#4 C3. 0.11. 5-D
#5 C2. 0.77. 5-D
#6 C2. 0.40. 5-B

---

Or using data.table

library(data.table)
setDT(df1)[, Type := factor(Type, levels = c('C1.', 'C3.', 'C2.'))]
setorder(df1, Type, -freq)

---

In base R, we can do

df1[order(factor(df1$Type, levels = c('C1.', 'C3.', 'C2.')), -df1$freq),]

data

df1 <- structure(list(Type = c("C3.", "C1.", "C2.", "C1.", "C2.", "C3."
), freq = c("0.34.", "0.90.", "0.40.", "0.65.", "0.77.", "0.11."
), Val = c("10-A", "4-A", "5-B", "3-C", "5-D", "5-D")), 
 class = "data.frame", row.names = c(NA, 
-6L))

• Lou_A: I’m working with the "dplyr" library. My final df is arranging freq correctly, but the order of the Type is yielding C1, C2, C3, and not C1, C3, C2. I wonder if there’s something missing.
• akrun: @Orion11 If you neeed to change the column, assign the factor output to that column and then it should work
• Lou_A: Ok. I got it to work. I was missing the "$Type" part. Thank you very much.