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rlistvariablesextract

Extract items in a list using variable names in R

I'm parsing a JSON using the RJSONIO package.

The parsed item contains nested lists.

Each item in the list can be extracted using something like this:

dat_raw$`12`[[31]]

which correctly returns the string stored at this location (in this example, the '12' refers to the month and [[31]] to day).

"31-12-2021"

I now want to run a for loop to sequentially extract the date for every month. Something like this:

for (m in 1:12) {

     print(dat_raw$m[[31]])

}

This, naturally, returns a NULL because there is no $m[[31]] in the list. Instead, I'd like to extract the objects stored at $`1`[[31]], $`2`[[31]], ... $`12`[[31]].

There must be a relatively easy solution here but I haven't managed to crack it. I'd value some help. Thanks.

EDIT: I've added a screenshot of the list structure I'm trying to extract. The actual JSON object is quite large for a dput() output. Hope this helps

dat_raw data structure

So, to get the date in this list, I'd use something like dat_raw$data$`1`[[1]]$date$gregorian$date.

What I'm trying to do is run a loop to extract multiple items of the list by cycling through $data$`1`[[1]]$..., $data$`2`[[1]]$... ... $data$`12`[[1]]$... using $data$m[[1]]$... in a for loop where m is the month.

Solution

  • Instead of dat_raw$`12`[[31]], you can have dat_raw[[12]][[31]] if 12 is the 12th element of the JSON. So your for loop would be:

    for (m in 1:12) {
     print(dat_raw[[m]][[31]])
}