Reorder frequency table in R

February 12, 2024

I have a column of grades in a dataframe. I can generate a frequency table of these grades. However, I would like to change the order of the columns in the frequency table from A, A*, B, C, D, E, U to A*, A, B, C, D, E, U (an A* grade should appear first in list).

Not sure if this is possible. But it would be super helpful as I want to make a barplot of the data.

Thanks
Martyn

>Solution :

In this case, since table() is a named data structure you can simply specify the order using the desired order of names for indexing:

# Data
df <- data.frame(grade = rep(c("A", "A*", "B", "C", "D", "E", "U"), each = 10))

table(df$grade)[c("A*", "A", "B", "C", "D", "E", "U")]

# A*  A  B  C  D  E  U 
# 10 10 10 10 10 10 10

So in a barplot:

ordr <- c("A*", "A", "B", "C", "D", "E", "U")

barplot(table(df$grade)[ordr])

For other cases using an unnamed vector, one would would need to use match:

grades <- c("A", "A*", "B", "C", "D", "E", "U")
ordr <- c("A*", "A", "B", "C", "D", "E", "U")

grades[match(grades, ordr)]
# [1] "A*" "A"  "B"  "C"  "D"  "E"  "U"