How to convert object variable into string inside a function

Question

I have the following list of vectors

v1 <-  c("foo","bar")
v2 <-  c("qux","uip","lsi")

mylist <- list(v1,v2)

mylist
#> [[1]]
#> [1] "foo" "bar"
#> 
#> [[2]]
#> [1] "qux" "uip" "lsi"

What I want to do is to apply a function so that it prints the this string:

v1:foo,bar
v2:qux,uip,lsi

So it involves two step: 1) Convert object variable to string and 2) make the vector into string. The latter is easy as I can do this:

make_string <- function (content_vector) {
  cat(content_vector,sep=",") 
}

make_string(mylist[[1]])
# foo,bar
make_string(mylist[[2]])
# qux,uip,lsi

I am aware of this solution, but I don't know how can I turn the object name into a string within a function so that it prints like my desired output.

I need to to this inside a function, because there are many other output I need to process.

@akrun That's why I post. I don't know how could I turn v1 and v2 into string inside make_string. — pdubois
– pdubois, Commented Jul 26, 2017 at 7:55
okay, then we need to pass 'v1' and 'v2' bcz when you pass mylist[[1]] there is no 'v1' — akrun
– akrun, Commented Jul 26, 2017 at 7:56

akrun · Accepted Answer · 2017-07-26 08:03:30Z

3

We can use

cat(paste(c('v1', 'v2'), sapply(mylist, toString), sep=":", collapse="\n"), '\n')
#v1:foo, bar
#v2:qux, uip, lsi

If we need to pass the original object i.e. 'v1', 'v2'

make_string <- function(vec){
    obj <- deparse(substitute(vec))

    paste(obj, toString(vec), sep=":")
} 

make_string(v1)
#[1] "v1:foo, bar"

edited Jul 26, 2017 at 8:03

answered Jul 26, 2017 at 7:47

akrun

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5 Comments

pdubois Over a year ago

in your method v1 and v2 is hard coded as string. But I need to convert from object to string.

akrun Over a year ago

@pdubois DId you meant to assign it to two vector objects

pdubois Over a year ago

I mean I need v1, v2 to be passed as object not string. See my update.

pdubois Over a year ago

Great. Thanks a million. Last question. How can I use purrr to apply make_string for all object in mylist?

akrun Over a year ago

@pdubois But, in that case, there should be some indication of v1', v2`, as of now, there is nothing in mylist that relates to the original objects

meenaparam · Accepted Answer · 2017-07-26 08:10:06Z

1

If you want to use a list, you can name the objects in the list to be able to use them in a function. Remove the cat if you just want a string to be returned.

v1 <-  c("foo","bar")
v2 <-  c("qux","uip","lsi")

# objects given names here
mylist <- list("v1" = v1, "v2" = v2)

# see names now next to the $
mylist
$v1
[1] "foo" "bar"

$v2
[1] "qux" "uip" "lsi"

make_string <- function (content_vector) {
    vecname <- names(content_vector)
    cat(paste0(vecname, ":", paste(sapply(content_vector, toString), sep = ",")))
}

make_string(mylist[1])
v1:foo, bar

make_string(mylist[2])
v2:qux, uip, lsi

answered Jul 26, 2017 at 8:10

meenaparam

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