Extract string from JSON parsed character vector

Question

Could anyone please help me and explain how can I extract a string from a character vector that contains special characters in it?

I'm working with a vector like this:

txt <- c("{\"label\":\"Describes me best\",\"multiplier\":1}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
"{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
"{\"label\":\"Describes me best\",\"multiplier\":1}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
"{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Describes me best\",\"multiplier\":1}", 
"{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"
)

> txt
 [1] "{\"label\":\"Describes me best\",\"multiplier\":1}"       "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"
 [3] "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}" "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"
 [5] "{\"label\":\"Describes me best\",\"multiplier\":1}"       "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"
 [7] "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}" "{\"label\":\"Describes me best\",\"multiplier\":1}"      
 [9] "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}" "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"

I'd like to extract only the Describes me best and Somewhat describes me parts dropping the rest.

I was trying to adapt the str_match() solution as presented here https://stackoverflow.com/a/39086448/6925293, but probably due to multiple special characters {\" etc, I can't make it work.

This is JSON content, and you should be using a JSON parser, _not_ regex. — Tim Biegeleisen, Sep 26 '22 at 10:07
True, this data comes from JSON. Didn't realize it makes a difference. Any idea how can I extract it? — blazej, Sep 26 '22 at 10:08
How did you pull the data, within R or did you import as such into your R environment? — Chamkrai, Sep 26 '22 at 10:13
@TimBiegeleisen thank you for catching this. I edited my original question title. — blazej, Sep 26 '22 at 10:18

score 4 · Accepted Answer · answered Sep 26 '22 at 10:25

4

Since these are JSON strings, you can use the jsonStrings package:

library(jsonStrings)

x <- "{\"label\":\"Describes me best\",\"multiplier\":1}"
jstring <- jsonString$new(x)
jstring$at("label")
# "Describes me best"

answered Sep 26 '22 at 10:25

Stéphane Laurent

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How would you use jsonString() with a character vector. Do you need a loop/map, right? Something like: 1:length(txt) |> purrr::map(~{ jstring <- jsonString$new(txt[.x]) jstring$at("label") }) – Gorka Sep 26 '22 at 10:56
1

@Gorka Yes, or sapply/vapply – Stéphane Laurent Sep 26 '22 at 12:46

score 0 · Answer 2 · answered Sep 26 '22 at 10:13

Is this what you need?

  txt <- c("{\"label\":\"Describes me best\",\"multiplier\":1}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
           "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
           "{\"label\":\"Describes me best\",\"multiplier\":1}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", 
           "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Describes me best\",\"multiplier\":1}", 
           "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}", "{\"label\":\"Somewhat describes me\",\"multiplier\":0.5}"
  )
  
  
# With gsub you can catch between () a pattern, and get it with \\1
  gsub(pattern = '.*"(.*)",.*', replacement = "\\1", x = txt)

#>  [1] "Describes me best"     "Somewhat describes me" "Somewhat describes me"
#>  [4] "Somewhat describes me" "Describes me best"     "Somewhat describes me"
#>  [7] "Somewhat describes me" "Describes me best"     "Somewhat describes me"
#> [10] "Somewhat describes me"

^{Created on 2022-09-26 with reprex v2.0.2}

While this solution does what I asked for, the `jsonStrings()` one gives me more flexibility and I'll accept that one. Still, thank you for the `gsub()` - I'll use it elsewhere. — blazej, Sep 26 '22 at 11:03
No worries. Thanks for the comment. I agree the jsonStrings is better when dealing with JSON strings. I tend to use gsub when the input is not always well formed JSON. Cheers. — Gorka, Sep 26 '22 at 11:13

Extract string from JSON parsed character vector

2 Answers2