quick tips: within function assignment and specific object removal

January 31, 2012
By

[This article was first published on mintgene » R, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
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If you’re familiar with the faster iterations on objects such as lapply, sapply, or apply for matrices, you might get surprised that the function call saves new assignments only locally.

# to assign global variable within function use "<<-" operator
lapply(1:10, function(i) {
    if (i != 1) {
        global.var <<- global.var + i; return(NULL)
    } else {
        global.var <<- i; return(NULL)
    }
})

cat(global.var)
# 55

# another neat trick is the multiple assignment to objects
global.var -> global.var.A -> global.var.B
global.var == global.var.B

# TRUE

One of my favorite lines in R comes from the fact the language environment devours the memory. To focus on particular objects (such as when you need to save it as *.rda), replace the search term within grepl function for the one that you wish to keep.

ls()
# "global.var"   "global.var.A" "global.var.B"

rm(list = ls()[!grepl("global.var.A", ls())])

# refresh memory
gc()

ls()
#  "global.var.A"

Cheers, mintgene.

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