Why does mapply repeat the same list multiple times?

Question

Please let me start by providing synthetic data set that shows the issues:

Do <- rep(c(0,2,4,6,8,10,15,20,30,40,45,50,55,60,65,70,80,85,90,92,94,96,98,100), each=16,times=16)
Cl <- rep(c("K", "Y","M","C"), each= 384, times=4)
In <- rep(c("A", "S"), each=3072)
Sa <- rep(c(1,2), each=1536)
Data <- rnorm(6144)
DataFrame <- cbind.data.frame(Do,Cl,In,Sa,Data); head(DataFrame)
rm(Do,Cl,In,Sa,Data)
attach(DataFrame)

Next, I split the 'DataFrame' object into multiple lists to avoid unpredictable recycling. Basically, I am placing each data subset in a separate list so that cycling is predictable and that produced the correct output in my simulator.

DFSplit <- split(DataFrame[ , "Data"], list(Do, Cl, In, Sa))

The 'DFSplit' object has 384 lists

length(names(DFSplit))

Then I created the function 'ids' to identify the lists names

ids <- function(Do, Cl, In, Sa){
    grep( paste( "^" , Do, "\\.",
                Cl, "\\.",
                In,
                "\\.", Sa,sep=""),
         names(DFSplit), value = TRUE)}

mapply(ids, Do, Cl, In, Sa, SIMPLIFY = FALSE)

I understand that each of 'ids' arguments' length is 6144. mapply produces 384 lists each repeated 16 times. How can I change the ids function so that mapply doesn't repeat the same name 16 times. As an ugly and highly costly solution I used unique; i need a better fundamental solution.

unique(mapply(ids, Do, Cl, In, Sa, SIMPLIFY = FALSE))

I also created a function to operate on the 'DFSplit' lists. It has the same issue as the previous function. The thing is, it accepts the previous function as an input.

dG <- function(Do,Cl, In, Sa){
    dg <- 100*
                (1-10^-( DFSplit[[ids(Do,  Cl, In, Sa)]] - DFSplit[[ids(0, Cl, In, Sa)]])) /
                (1-10^-( DFSplit[[ids(100, Cl, In, Sa)]] - DFSplit[[ids(0, Cl, In, Sa)]])) - Do
    dg}

mapply(dG, Do, Cl, In, Sa, SIMPLIFY = FALSE)

What I am trying to do, unsuccessfully if I may say, is to apply the dG function inside each of the 384 lists. I acknowledge that dG function also needs to be modified and I don't know how. I want the input to the dG function to be the names of 384 lists each containing 16 numbers. I want the output to be 384 list with the dG applied.

Please feel free to suggest a different solution all together. The important thing is I need to apply the 'dG' function to the data set.

Answer 1

Please take a closer look at what you are giving mapply Each object is of length 6144.

  > length(Do)
  [1] 6144
  > length(Cl)
  [1] 6144
  > length(In)
  [1] 6144
  > length(Sa)
  [1] 6144
  > 

You are giving mapply 6144 tuples and asking it to iterate over each.
It is giving you back a list of 6144 elements.

It is exactly what you are telling it to do

---

Also, just copying and pasting your code yields a list 6144 long, each element containing 16 elements.

  .
  .
  [[6141]]
   [1]  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  1.421085e-14
  [12]  0.000000e+00  0.000000e+00  0.000000e+00 -1.421085e-14  0.000000e+00

  [[6142]]
   [1]  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  1.421085e-14
  [12]  0.000000e+00  0.000000e+00  0.000000e+00 -1.421085e-14  0.000000e+00

  [[6143]]
   [1]  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  1.421085e-14
  [12]  0.000000e+00  0.000000e+00  0.000000e+00 -1.421085e-14  0.000000e+00

  [[6144]]
   [1]  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  0.000000e+00  1.421085e-14
  [12]  0.000000e+00  0.000000e+00  0.000000e+00 -1.421085e-14  0.000000e+00

Therefore, not 6144 of 1 element as you describe.

You received two very good pieces of advice, one form @Arun and one from @Paul Hiemstra.

Perhaps you can try describing what it is you are attempting to accomplish and folks here can better assist you. Also, please dont forget to look back on your previous questions and up vote and thank those who have given you helpful answers.