How to extract select and filter query from url in R

Question

This is the url from which I want to extract the string in select query and in filter query:

http://services.odata.org/V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People?$select=ID,CLASS,FIRST_NAME,LAST_NAME&$filter=FirstName eq 'Angel' or FirstName eq 'Clyde'

I would like to extract select and filter query values in 2 strings. I have tried these:

res <- str_match(a, "STR1 (.*?) STR2")

I have tried extracting values using string handling, as shown in this related question (Extract string between /), but I was not able to extract the values. Is there any other method which can help?

sebastian-c · Accepted Answer · 2017-09-18 12:20:25Z

6

httr has a parse_url function:

library(httr)

myurl <- "http://services.odata.org/V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People?$select=ID,CLASS,FIRST_NAME,LAST_NAME&$filter=FirstName eq 'Angel' or FirstName eq 'Clyde'"

parse_url(myurl)

Output:

$scheme
[1] "http"

$hostname
[1] "services.odata.org"

$port
NULL

$path
[1] "V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People"

$query
$query$`$select`
[1] "ID,CLASS,FIRST_NAME,LAST_NAME"

$query$`$filter`
[1] "FirstName eq 'Angel' or FirstName eq 'Clyde'"


$params
NULL

$fragment
NULL

$username
NULL

$password
NULL

attr(,"class")
[1] "url"

answered Sep 18, 2017 at 12:20

sebastian-c

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pogibas · Accepted Answer · 2017-09-18 12:25:41Z

Solution by splitting url by $ and then extracting select and filter parts.

foo <- "http://services.odata.org/V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People?$select=ID,CLASS,FIRST_NAME,LAST_NAME&$filter=FirstName eq 'Angel' or FirstName eq 'Clyde'"
bar <- unlist(strsplit(foo, "\\$"))
bar
[1] "http://services.odata.org/V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People?"
[2] "select=ID,CLASS,FIRST_NAME,LAST_NAME&"                                              
[3] "filter=FirstName eq 'Angel' or FirstName eq 'Clyde'" 

resultSelect <- unlist(strsplit(gsub("select=|\\&$", "", grep("^select=", bar, value = TRUE)), ","))
resultFilter <- unlist(strsplit(gsub("filter=", "", grep("^filter=", bar, value = TRUE)), ","))

resultSelect
[1] "ID"         "CLASS"      "FIRST_NAME" "LAST_NAME" 

resultFilter
[1] "FirstName eq 'Angel' or FirstName eq 'Clyde'"

Tidier example using pipes and custom function:

URL <- "http://services.odata.org/V4/(S(cscsmmmc110sj01dvwgyolkm))/TripPinServiceRW/People?$select=ID,CLASS,FIRST_NAME,LAST_NAME&$filter=FirstName eq 'Angel' or FirstName eq 'Clyde'"
queries <- c("select", "filter")

extractQ <- function(x, url = URL) {
    library(magrittr)
    strsplit(url, "\\$") %>%
        unlist() %>%
        grep(paste0("^", x, "="), ., value = TRUE) %>%
        gsub(paste0(x, "=|\\&$"), "", .) %>%
        strsplit(",") %>%
        unlist()
}

sapply(queries, extractQ)

$select
[1] "ID"         "CLASS"      "FIRST_NAME" "LAST_NAME" 

$filter
[1] "FirstName eq 'Angel' or FirstName eq 'Clyde'"

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