R- For loop for non-sequential list

Question

This is probably a simple question, but I'm struggling finding a way to do the equivalent of "for (i in 1:10){ do something}" but with a list of strings. For example:

given a list of strings a = ("Joe", "John", "George") I'd want to do the following:

for (a in "Joe":"George"){
  url <- paste0(http://www.website.com/", a)
  readHTMLTable(url)
}

and have the function traverse through the list of names and hit the url with each name. Thanks.

Definitely use `lapply` instead of `for` so your results will be in a list. Also `:` between strings doesn't work; use the variable you stored them in. — alistaire, Oct 22 '16 at 02:49

score 0 · Accepted Answer · answered Oct 22 '16 at 02:56

0

You'd go with for (i in 1:length(a)) { etc } but yeah getting your head around apply functions is generally preferable for speed reasons.

answered Oct 22 '16 at 02:56

obrl_soil

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Idk how I never tried that, worked perfectly, thank you. So would the lapply be something along the lines of – chaseking123 Oct 22 '16 at 03:11
a <- lapply(table, function(x){ – chaseking123 Oct 22 '16 at 03:12
Sorry, I can't stop hitting enter. – chaseking123 Oct 22 '16 at 03:13
a <- lapply(table, function(x){ ?? }) – chaseking123 Oct 22 '16 at 03:14
`b <- lapply(a, FUN = function(x) { url <- paste0(http://www.website.com/", x) return(readHTMLTable(url)) }` would (i think) get you a list of tables, which you could then rbind into a data.frame or whatever. untested though – obrl_soil Oct 22 '16 at 03:53

score 0 · Answer 2 · answered Oct 22 '16 at 03:57

Use "" in paste0 function

a = c("Joe", "John", "George")

for (i in 1:length(a)){
  url <- paste0("http://www.website.com/", a)
      readHTMLTable(url)
}

lapply(a, function(x){paste0("http://www.website.com/", x)})
[[1]]
[1] "http://www.website.com/Joe"

[[2]]
[1] "http://www.website.com/John"

[[3]]
[1] "http://www.website.com/George"

sapply(a, function(x){paste0("http://www.website.com/", x)})

Joe                            John                          George 
"http://www.website.com/Joe"   "http://www.website.com/John" "http://www.website.com/George"

R- For loop for non-sequential list

2 Answers2