[R] Embedding lists in matrices and matrices in lists

[Michael Kogan]

Thanks, that was the solution! But in fact I didn't want to have this 
"list of lists" layer at all. And now I'm having trouble writing 
matrices into the database.  It's really really strange... If I write a 
matrix into the database manually everything works, but if I create a 
function which adds a matrix into the database and then run the function 
it fails... Look at this (sorry for the long code block, in fact you can 
skip the "sums" and "test_sums" functions):
> ######################test matrix#######################
> m1=matrix(c(
> 1,0,
> 0,1
> ),nrow=2, byrow=TRUE)
>
> #########################sums###########################
> sums=function(matrix)
> {
> c(sort(colSums(matrix)),sort(rowSums(matrix)))
> }
>
> ######################test_sums#########################
> test_sums=function(matrix)
> {
> liste=database[[nrow(matrix),ncol(matrix)]][[1]]
> w=1
> if(length(liste)>0){
>     for(i in 1:length(liste)){
>         if(all(sums(matrix)==sums(liste[[i]]))){
>             w0=0
>         }else{
>             w0=1}
>     w=w*w0}
> }else{
>     w=2}
> w
> }
>
> #####################write to db########################
> write_to_db=function(matrix){
> en=nrow(matrix)
> fn=ncol(matrix)
> if(test_sums(matrix)==1){
>     print("matrix isn't in the DB yet")
>     database[en,fn][[1]]=list(database[en,fn][[1]], matrix)
> }else if(test_sums(matrix)==2){
>     print("matrix isn't in the DB entry yet and DB is empty")
>     database[en,fn][[1]][[1]]=list(matrix)
> }else{
>     print("matrix already exists in the DB")
> }
> }
>
> ######################create database##################
> database=matrix(list(),2,2)
>
> ##trying to write a matrix into db using the function##
> write_to_db(m1)
> database
>
> ###writing a matrix into db without using a function###
> en=nrow(m1)
> fn=ncol(m1)
> if(test_sums(m1)==1){
>     print("matrix isn't in the DB yet")
>     database[en,fn][[1]]=list(database[en,fn][[1]], m1)
> }else if(test_sums(m1)==2){
>     print("matrix isn't in the DB entry yet and DB is empty")
>     database[en,fn][[1]][[1]]=list(m1)
> }else{
>     print("matrix already exists in the DB")
> }
> database
>
> ###########test whether matrix already is in db##########
> write_to_db(m1)
And the output is:
> [1] "matrix isn't in the DB entry yet and DB is empty"
>      [,1] [,2]
> [1,] NULL NULL
> [2,] NULL NULL
> [1] "matrix isn't in the DB entry yet and DB is empty"
>      [,1] [,2]  
> [1,] NULL NULL  
> [2,] NULL List,1
> [1] "matrix already exists in the DB"
So writing the matrix into the database using the function fails while 
writing it using the same commands but not through a function works! 
Maybe it's a problem with all these layers in the database matrix?

Petr PIKAL schrieb:
> Hi
>
> r-help-bounces at r-project.org napsal dne 19.08.2009 13:04:39:
>
>   
>> Strange, it doesn't work for me:
>>
>> Error in database[4, 4][[1]][1, ] : incorrect number of dimensions
>> Execution halted
>>
>> R version 2.9.0 (2009-04-17) on Arch Linux, no additional packages 
>> installed.
>>     
>
> database[4,4][[1]][,1]
>
> does not work for me either but it is result of your complicated structure 
> of nested lists
>
> This works
>
>   
>> database[4,4][[1]][[1]][,1]
>>     
> [1] 0 1 1 1
>
> See the structure
>
> Matrix of lists
>
>   
>> database
>>     
>      [,1] [,2] [,3] [,4]   [,5]
> [1,] NULL NULL NULL NULL   NULL
> [2,] NULL NULL NULL NULL   NULL
> [3,] NULL NULL NULL NULL   NULL
> [4,] NULL NULL NULL List,1 NULL
> [5,] NULL NULL NULL NULL   NULL
>
> List of lists
>   
>> database[4,4]
>>     
> [[1]]
> [[1]][[1]]
>      [,1] [,2] [,3] [,4]
> [1,]    0    1    1    1
> [2,]    1    0    1    1
> [3,]    1    1    0    1
> [4,]    1    1    1    0
>
> List which contains your matrix
>
>   
>> database[4,4][[1]]
>>     
> [[1]]
>      [,1] [,2] [,3] [,4]
> [1,]    0    1    1    1
> [2,]    1    0    1    1
> [3,]    1    1    0    1
> [4,]    1    1    1    0
>
> Here is your matrix
>
>   
>> database[4,4][[1]][[1]]
>>     
>      [,1] [,2] [,3] [,4]
> [1,]    0    1    1    1
> [2,]    1    0    1    1
> [3,]    1    1    0    1
> [4,]    1    1    1    0
>   
>
> Regards
> Petr