Subassign-methods: Methods for "[<-" - Assigning to Subsets for 'Matrix'
In bedatadriven/renjin-matrix: Sparse and Dense Matrix Classes and Methods

Methods for "[<-", i.e., extraction or subsetting mostly of matrices, in package Matrix.

Note: Contrary to standard matrix assignment in base R, in x[..] <- val it is typically an error (see stop) when the type or class of val would require the class of x to be changed, e.g., when x is logical, say "lsparseMatrix", and val is numeric. In other cases, e.g., when x is a "nsparseMatrix" and val is not TRUE or FALSE, a warning is signalled, and val is “interpreted” as logical, and (logical) NA is interpreted as TRUE.

There are many many more than these:

x = "Matrix", i = "missing", j = "missing", value= "ANY": is currently a simple fallback method implementation which ensures “readable” error messages.
x = "Matrix", i = "ANY", j = "ANY", value= "ANY": currently gives an error
x = "denseMatrix", i = "index", j = "missing", value= "numeric": ...
x = "denseMatrix", i = "index", j = "index", value= "numeric": ...
x = "denseMatrix", i = "missing", j = "index", value= "numeric": ...

[-methods for subsetting "Matrix" objects; the index class; Extract about the standard subset assignment (and extraction).

set.seed(101)
(a <- m <- Matrix(round(rnorm(7*4),2), nrow = 7))

a[] <- 2.2 # <<- replaces **every** entry
a
## as do these:
a[,] <- 3 ; a[TRUE,] <- 4

m[2, 3]  <- 3.14 # simple number
m[3, 3:4]<- 3:4  # simple numeric of length 2

## sub matrix assignment:
m[-(4:7), 3:4] <- cbind(1,2:4) #-> upper right corner of 'm'
m[3:5, 2:3] <- 0
m[6:7, 1:2] <- Diagonal(2)
m

## rows or columns only:
m[1,] <- 10
m[,2] <- 1:7
m[-(1:6), ] <- 3:0 # not the first 6 rows, i.e. only the 7th
as(m, "sparseMatrix")