multi-dimensional list? List of lists? array of lists?

Question

(I am definitively using wrong terminology in this question, sorry for that - I just don't know the correct way to describe this in R terms...)

I want to create a structure of heterogeneous objects. The dimensions are not necessary rectangular. What I need would be probably called just "array of objects" in other languages like C. By 'object' I mean a structure consisting of different members, i.e. just a list in R - for example:

myObject <- list(title="Uninitialized title", xValues=rep(NA,50), yValues=rep(NA,50)) 

and now I would like to make 100 such objects, and to be able to address their members by something like

for (i in 1:100) {myObject[i]["xValues"]<-rnorm(50)}

or

for (i in 1:100) {myObject[i]$xValues<-rnorm(50)}

I would be grateful for any hint about where this thing is described.

Thanks in advance!

Solution 1

I did not realize that you were looking for creating other objects of same structure. You are looking for replicate.

my_fun <- function() {
    list(x=rnorm(1), y=rnorm(1), z="bla")
}
replicate(2, my_fun(), simplify=FALSE)

# [[1]]
# [[1]]$x
# [1] 0.3561663
# 
# [[1]]$y
# [1] 0.4795171
# 
# [[1]]$z
# [1] "bla"
# 
# 
# [[2]]
# [[2]]$x
# [1] 0.3385942
# 
# [[2]]$y
# [1] -2.465932
# 
# [[2]]$z
# [1] "bla"

Solution 2

are you looking for the name of this mythical beast or just how to do it? :) i could be wrong, but i think you'd just call it a list of lists.. for example:

# create one list object
x <- list( a = 1:3 , b = c( T , F ) , d = mtcars )

# create a second list object
y <- list( a = c( 'hi', 'hello' ) , b = c( T , F ) , d = matrix( 1:4 , 2 , 2 ) )

# store both in a third object
z <- list( x , y )

# access x
z[[ 1 ]] 

# access y
z[[ 2 ]]

# access x's 2nd object
z[[ 1 ]][[ 2 ]]

Solution 3

here is the example of solution I have for the moment, maybe it will be useful for somebody:

    NUM <- 1000 # NUM is how many objects I want to have
    xVal <- vector(NUM, mode="list")
    yVal <- vector(NUM, mode="list")
    title   <- vector(NUM, mode="list")
    for (i in 1:NUM) {
     xVal[i]<-list(rnorm(50))
     yVal[i]<-list(rnorm(50))
     title[i]<-list(paste0("This is title for instance #", i))
    }
   myObject <- list(xValues=xVal, yValues=yVal, titles=title)
   # now I can address any member, as needed:
   print(myObject$titles[[3]])
   print(myObject$xValues[[4]])  

Solution 4

If the dimensions are always going to be rectangular (in your case, 100x50), and the contents are always going to be homogeneous (in your case, numeric) then create a 2D array/matrix.

If you want the ability to add/delete/insert on individual lists (or change the data type), then use a list-of-lists.

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