Overriding parts of function definition

Question

With assignInNamespace you can override package functions. That works fine, but I have to override only one line out of 200 function lines. So I have to copy & paste much code. :(

Is there a way to override only parts of a function? Only a variable or another function inside the function?

Answer 1

Yes. You can use body<- . Here's a simple example that changes the last line of setNames

setNames                          ## original function
# function (object = nm, nm) 
# {
#     names(object) <- nm
#     object
# }
# <bytecode: 0x45367a8>
# <environment: namespace:stats>
as.list(body(setNames))           ## look at the function body as a list
# [[1]]
# `{`
# 
# [[2]]
# names(object) <- nm
#
# [[3]]
# object
#
body(setNames)[[3]] <- quote(nm)  ## replace the last line with 'nm'
setNames
# function (object = nm, nm) 
# {
#     names(object) <- nm
#     nm
# }
#<environment: namespace:stats>

Note that you can use grep to find where a certain variable is located in the function body

grep("object", body(setNames))
# [1] 2 3