Multi tool use

R - loop iteratively through lists and create a dataframe

I have a long list of lists (> 100k) and need to iteratively loop through each list and extract the "id" - which i can do easily by constructing lapply in a for loop.

lapply

Here is an example of the lists:

l1 <- list(id="002e2b45555652749339ab9c34359fb6", key="2", value="xx")
l2 <- list(id="002e2b433226527493jsab9c34353fb6", key="4", value="zz")
l3 <- list(list1, list2)


I do the looping with:

for(i in 1:20) {
lapply(l3$id[[i]][1], function (x) print(x))
}


Basically printing all the elements of each list of the id - which is nice.
I ultimately want to construct a matrix / dataframe with all the "ids" in rows. What bugs me is, the print in my loop works well, printing out all ids from all the lists - although I cannot bind my rows to a dataframe or a matrix etc. i was trying out something like - ain't doing what i want (although not getting an error etc.)

for(i in 1:20) {
lapply(l3$id[[i]][1], function (x) rbind(x))
}


SO the desired output shall be (preferrably as a dataframe).

[1] "002e2b45555652749339ab9c3400cc52"
[1] "002e2b45555652749339ab9c34040525"


2 Answers
2

using base R:

s=aggregate(.~ind,stack(setNames(l3,1:length(l3))),identity)
ind values.1 values.2 values.3
1 1 002e2b45555652749339ab9c34359fb6 2 xx
2 2 002e2b433226527493jsab9c34353fb6 4 zz


if you just need the id's

s$values[,1]
[1] "002e2b45555652749339ab9c34359fb6" "002e2b433226527493jsab9c34353fb6"


If you want a vector of the IDs you can do

sapply(l3, "[[", "id")


or using tidyverse functions

purrr::map_chr(l3, "id")


No need for loops for stuff like this in R.

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