# [R] Function sort.data.frame

Kevin Wright kwright at eskimo.com
Fri Sep 24 16:24:10 CEST 2004

```I can never remember how to use "order" to sort the rows of a data frame,
so like any good, lazy programmer, I decided to write my own function.

The idea is to specify a data.frame and a one-sided formula with +/-
indicating ascending/descending.  For example:
sort.data.frame(~ +nitro -Variety, Oats)

Since sorting of a data.frame is an oft-asked question on this list, I am
posting my function in hopes that others may find it useful.

Computing 'on the language' (formulas) is not my strongest point, so the
function can probably be improved.  A similar idea could be used for
matrix objects.  Feedback is welcome.

Kevin Wright

sort.data.frame <- function(form,dat){
# Author: Kevin Wright
# Some ideas from Andy Liaw
#   http://tolstoy.newcastle.edu.au/R/help/04/07/1076.html

# Use + for ascending, - for decending.
# Sorting is left to right in the formula

# Useage is either of the following:
# sort.data.frame(~Block-Variety,Oats)
# sort.data.frame(Oats,~-Variety+Block)

# If dat is the formula, then switch form and dat
if(inherits(dat,"formula")){
f=dat
dat=form
form=f
}
if(form[[1]] != "~")
stop("Formula must be one-sided.")

# Make the formula into character and remove spaces
formc <- as.character(form[2])
formc <- gsub(" ","",formc)
# If the first character is not + or -, add +
if(!is.element(substring(formc,1,1),c("+","-")))
formc <- paste("+",formc,sep="")
# Extract the variables from the formula
vars <- unlist(strsplit(formc, "[\\+\\-]"))
vars <- vars[vars!=""] # Remove spurious "" terms

# Build a list of arguments to pass to "order" function
calllist <- list()
pos=1 # Position of + or -
for(i in 1:length(vars)){
varsign <- substring(formc,pos,pos)
pos <- pos+1+nchar(vars[i])
if(is.factor(dat[,vars[i]])){
if(varsign=="-")
calllist[[i]] <- -rank(dat[,vars[i]])
else
calllist[[i]] <- rank(dat[,vars[i]])
}
else {
if(varsign=="-")
calllist[[i]] <- -dat[,vars[i]]
else
calllist[[i]] <- dat[,vars[i]]
}
}
dat[do.call("order",calllist),]

}

d = data.frame(b=factor(c("Hi","Med","Hi","Low"),levels=c("Low","Med","Hi"),
ordered=TRUE),
x=c("A","D","A","C"),y=c(8,3,9,9),z=c(1,1,1,2))
sort.data.frame(~-z-b,d)
sort.data.frame(~x+y+z,d)
sort.data.frame(~-x+y+z,d)
sort.data.frame(d,~x-y+z)

```