r - Reorder a column in a dataframe to a specified order

Question

I have a data frame, where every row has a value, and every block of 100 rows has an index (between 1 and 10). I would like to sort the index blocks in a particular order, but am unsure how to do that:

N=1000
value = runif(N, min=0, max=100)
index = rep(1:10, each=100)
DF=data.frame(value,index)
ord = c(1,4,6,3,7,9,8,2,5,10)

So basically, I would like the index column of DF to be ordered in blocks of the order specified in ord, instead of the index column of DF being ordered as 1,2,3,4,5,6,7,8,9,10.

Any advice would be appreciated!

Answer 1

You could simply convert index to factor and set the levels as in ord order and then sort the data as in

DF$index <- factor(DF$index, levels = ord)
DF[order(DF$index), ]

If you don't want to "alter your original data" you could simply create a separate index as in

indx <- factor(DF$index, levels = ord) 
DF[order(indx), ]

Additional otion is to order your data set by reference using setorder from the data.table package

library(data.table)
setorder(setDT(DF)[, index := factor(index, levels = ord)], index)