Order data.frame by factor based on integers

Question

I have a data.frame in which one of the columns, originally containing integer values, was converted to a factor (upstream of any data that I have).

I'd like to sort the data.frame based on this factor, but have the results sorted such that the order of this factor is "1 2 3" instead of "1 11 12," as is what happens when I use order with no other manipulations:

sample <- data.frame(a = c(1,2,2,3,4), b= factor(c("1","12","11","2","3")))
sample
  a  b
1 1  1
2 2 12
3 2 11
4 3  2
5 4  3
sample[order(sample$b),]
  a  b
1 1  1
3 2 11
2 2 12
4 3  2
5 4  3

Since I want that column to remain a factor in my final dataset, I am hesitant to convert the column to an integer (because of issues with as.integer and as.numeric when applied to factors). I also have nearly 100 levels in this factor, so manually redefining the levels of the factor in a way that requires me to write out each level is not ideal either.

akrun akrun · Accepted Answer · 2015-10-09T03:44:07

We can order the dataset rows after converting the 'b' column to numeric class, but the class of the 'b' still remains as factor.

sample1 <- sample[order(as.numeric(as.character(sample$b))),]
row.names(sample1) <- NULL
str(sample1)
#'data.frame':   5 obs. of  2 variables:
#$ a: num  1 3 4 2 2
#$ b: Factor w/ 5 levels "1","11","12",..: 1 4 5 2 3

sample1
#  a  b
#1 1  1
#2 3  2
#3 4  3
#4 2 11
#5 2 12

Order data.frame by factor based on integers

1 Answers