# Processing nested lists

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So perhaps you have all figured this out already, but I was excited to figure out how to finally neatly get all the data frames, lists, vectors, etc. out of a nested list. It is as easy as nesting calls to the apply family of functions, in the case below, using plyr’s apply like functions. Take this example:

# Nested lists code, an example # Make a nested list mylist <- list() mylist_ <- list() for(i in 1:5) { for(j in 1:5) { mylist[[j]] <- i*j } mylist_[[i]] <- mylist } # return values from first part of list laply(mylist_[[1]], identity) [1] 1 2 3 4 5 # return all values laply(mylist_, function(x) laply(x, identity)) 1 2 3 4 5 [1,] 1 2 3 4 5 [2,] 2 4 6 8 10 [3,] 3 6 9 12 15 [4,] 4 8 12 16 20 [5,] 5 10 15 20 25 # perform some function, in this case sqrt of each value laply(mylist_, function(x) laply(x, function(x) sqrt(x))) 1 2 3 4 5 [1,] 1.000000 1.414214 1.732051 2.000000 2.236068 [2,] 1.414214 2.000000 2.449490 2.828427 3.162278 [3,] 1.732051 2.449490 3.000000 3.464102 3.872983 [4,] 2.000000 2.828427 3.464102 4.000000 4.472136 [5,] 2.236068 3.162278 3.872983 4.472136 5.000000

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