Parse URLencoded GET string in R into a list

Question

I need an an elegant way in R to take a urlencoded string such as: test.aspx?title=Pancreas%20Cancer&startYear=2000&dataCSV=461%2C520%2C559%2C627%2C1065%2C1217%2C1323%2C1512%2C2160%2C2554%2C2707%2C3000%2C3495%2C4163%2C4927%2C5237%2C4785%2C5559%2C6490%2C7559%2C5106%2C6358%2C6824%2C7980%2C4873%2C6715%2C7038%2C8156%2C4863%2C6460%2C7244%2C9161%2C5237%2C6176%2C6531%2C9068%2C5628%2C5983%2C5871%2C7951%2C6060%2C6089%2C5520%2C6627%2C5722%2C6099%2C5586%2C5822%2C4185%2C4909%2C5053%2C5273%2C5227%2C6077%2C6681%2C7977%2C

And get a list back that uses the keys sent in the URL the values sent:

list ( title = "Pancreas Cancer",
       startYear = 2000,
       dataCSV = matrix ( c(461, 520....etc), nrows = X, byrow = TRUE)
 );

Is there anyway to do this easily in R?

URLdecode was my first thought but it just takes out the url encoded characters like %2c and replaces them with their "readable" value like comma or space. I need something that actually parses that string into key value pairs. — Brent
– Brent, Commented Dec 11, 2013 at 11:06

hadley · Accepted Answer · 2013-12-11 13:28:57Z

3

httr provides a function to parse urls, of which this is an example:

url <- "test.aspx?title=Pancreas%20Cancer&startYear=2000&dataCSV=461%2C520%2C559%2C627%2C1065%2C1217%2C1323%2C1512%2C2160%2C2554%2C2707%2C3000%2C3495%2C4163%2C4927%2C5237%2C4785%2C5559%2C6490%2C7559%2C5106%2C6358%2C6824%2C7980%2C4873%2C6715%2C7038%2C8156%2C4863%2C6460%2C7244%2C9161%2C5237%2C6176%2C6531%2C9068%2C5628%2C5983%2C5871%2C7951%2C6060%2C6089%2C5520%2C6627%2C5722%2C6099%2C5586%2C5822%2C4185%2C4909%2C5053%2C5273%2C5227%2C6077%2C6681%2C7977%2C"

library(httr)
str(parse_url(url)$query)

answered Dec 11, 2013 at 13:28

hadley

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2 Comments

sckott Over a year ago

Ah, parse_url is what I was trying to remember, should have since I've used it before, thanks @hadley

Brent Over a year ago

I'll give this a try in the code later today and post my results.

sckott · Accepted Answer · 2013-12-10 21:37:55Z

1

This is a start, not very general really either probably

library(RCurl)
string <- "http://stuff.com/test.aspx?title=Pancreas%20Cancer&startYear=2000&dataCSV=461%2C520%2C559%2C627%2C1065%2C1217%2C1323%2C1512%2C2160%2C2554%2C2707%2C3000%2C3495%2C4163%2C4927%2C5237%2C4785%2C5559%2C6490%2C7559%2C5106%2C6358%2C6824%2C7980%2C4873%2C6715%2C7038%2C8156%2C4863%2C6460%2C7244%2C9161%2C5237%2C6176%2C6531%2C9068%2C5628%2C5983%2C5871%2C7951%2C6060%2C6089%2C5520%2C6627%2C5722%2C6099%2C5586%2C5822%2C4185%2C4909%2C5053%2C5273%2C5227%2C6077%2C6681%2C7977%2C"
string <- URLdecode(string)
string <- strsplit(string, "\\?")[[1]][[2]]
lapply(strsplit(string, "&")[[1]], function(x){
  tmp <- strsplit(x, "=")
  val <- tmp[[1]][[2]]
  names(val) <- tmp[[1]][[1]]
  as.list(val)
})

[[1]]
[[1]]$title
[1] "Pancreas Cancer"


[[2]]
[[2]]$startYear
[1] "2000"


[[3]]
[[3]]$dataCSV
[1] "461,520,559,627,1065,1217,1323,1512,2160,2554,2707,3000,3495,4163,4927,5237,4785,5559,6490,7559,5106,6358,6824,7980,4873,6715,7038,8156,4863,6460,7244,9161,5237,6176,6531,9068,5628,5983,5871,7951,6060,6089,5520,6627,5722,6099,5586,5822,4185,4909,5053,5273,5227,6077,6681,7977,"

answered Dec 10, 2013 at 21:37

sckott

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2 Comments

Brent Over a year ago

Thanks! I was hoping R had some package I was unaware of that made this more concise, but this works great!

Brent Over a year ago

The last step for readers is to take the dataCSV and convert it into a vector. You do that like this: c(as.numeric(strsplit(outputFromLapply[[3]][[1]],',')[[1]])); Then you convert that to a matrix by passing that output to the matrix method and setting ncol, nrow, and by row = TRUE

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