R Under development (unstable) (2023-11-05 r85474 ucrt) -- "Unsuffered Consequences"
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> ## for R_DEFAULT_PACKAGES=NULL :
> library(utils)
> 
> library(Matrix)
> 
> ####  Read / Write  (sparse) Matrix objects ----------------------
> 
> ### Rebuild the 'mm' example matrix, now in KNex data
> 
> ### This is no longer really important, as we now use
> ### ../data/KNex.R  which creates the S4 object *every time*
> data(KNex, package = "Matrix")
> 
> ## recreate 'mm' from list :
> sNms <- c("Dim", "i","p","x")
> L <- lapply(sNms, function(SN) slot(KNex$mm, SN)); names(L) <- sNms
> mm2 <- new(class(KNex$mm))
> for (n in sNms) slot(mm2, n) <- L[[n]]
> 
> stopifnot(validObject(mm2),
+           identical(mm2, KNex$mm))
> L$y <- KNex$y
> ## save(L, file = "/u/maechler/R/Pkgs/Matrix/inst/external/KNex_slots.rda")
> 
> 
> ## recreate 'mm' from ASCI file :
> mmT <- as(KNex$mm, "TsparseMatrix")
> str(mmT)
Formal class 'dgTMatrix' [package "Matrix"] with 6 slots
  ..@ i       : int [1:8755] 0 2 25 27 163 165 1258 1261 1276 1278 ...
  ..@ j       : int [1:8755] 0 0 0 0 0 0 0 0 0 0 ...
  ..@ Dim     : int [1:2] 1850 712
  ..@ Dimnames:List of 2
  .. ..$ : NULL
  .. ..$ : NULL
  ..@ x       : num [1:8755] 0.277 0.277 0.277 0.277 0.277 ...
  ..@ factors : list()
> mm3 <- cbind(i = mmT@i, j = mmT@j, x = mmT@x)
> write.table(mm3, file = "mm-Matrix.tab", row.names=FALSE)# -> ASCII version
> 
> str(mmr <- read.table("mm-Matrix.tab", header = TRUE))
'data.frame':	8755 obs. of  3 variables:
 $ i: int  0 2 25 27 163 165 1258 1261 1276 1278 ...
 $ j: int  0 0 0 0 0 0 0 0 0 0 ...
 $ x: num  0.277 0.277 0.277 0.277 0.277 ...
> mmr$i <- as.integer(mmr$i)
> mmr$j <- as.integer(mmr$j)
> 
> mmN <- with(mmr, new("dgTMatrix", Dim = c(max(i)+1:1,max(j)+1:1),
+                      i = i, j = j, x = x))
> 
> stopifnot(identical(mmT, mmN)) # !!
> ## weaker (and hence TRUE too):
> stopifnot(all.equal(as(mmN, "matrix"),
+                     as(mmT, "matrix"), tolerance=0))
> 
> mm <- as(mmN, "CsparseMatrix")
> stopifnot(all.equal(mm, KNex$mm))
> ## save(mm, file = "....../Matrix/data/mm.rda", compress = TRUE)
> 
> 
> A <- Matrix(c(1,0,3,0,0,5), 10, 10, sparse = TRUE) # warning about [6] vs [10]
Warning message:
In Matrix(c(1, 0, 3, 0, 0, 5), 10, 10, sparse = TRUE) :
  data length [6] is not a sub-multiple or multiple of the number of rows [10]
> (fname <- file.path(tempdir(), "kk.mm"))
[1] "D:\\temp\\RtmpMh7dJ3/kk.mm"
> writeMM(A, fname)
NULL
> (B  <- readMM(fname))
10 x 10 sparse Matrix of class "dgTMatrix"
                         
 [1,] 1 . 3 1 . 3 1 . 3 1
 [2,] . 5 . . 5 . . 5 . .
 [3,] 3 1 . 3 1 . 3 1 . 3
 [4,] . . 5 . . 5 . . 5 .
 [5,] . 3 1 . 3 1 . 3 1 .
 [6,] 5 . . 5 . . 5 . . 5
 [7,] 1 . 3 1 . 3 1 . 3 1
 [8,] . 5 . . 5 . . 5 . .
 [9,] 3 1 . 3 1 . 3 1 . 3
[10,] . . 5 . . 5 . . 5 .
> validObject(B)
[1] TRUE
> Bc <- as(B, "CsparseMatrix")
> stopifnot(identical(A, Bc))
> 
> fname <- system.file("external", "wrong.mtx", package = "Matrix")
> r <- try(readMM(fname))
Error : readMM(): row indices 'i' are not in 1:nrow[=2]
> stopifnot(inherits(r, "try-error"), length(grep("readMM.*row.*1:nr", r)) == 1)
> ## gave a much less intelligible error message
> 
> proc.time()
   user  system elapsed 
   1.48    0.25    1.71