# ------------------------------------------
# A «bycol» matrix
#
m_by_col <- matrix( c( 1, 2, 3, 11,
22, 33, 111, 222,
333,1111,2222,3333),
nrow=3,
ncol=4,
byrow=FALSE) # default
show(m_by_col)
# [,1] [,2] [,3] [,4]
# [1,] 1 11 111 1111
# [2,] 2 22 222 2222
# [3,] 3 33 333 3333
n <- m_by_col[c(1,3,5,7)]
show(n)
# [1] 1 3 22 111
# ------------------------------------------
# A «byrow» matrix
m_by_row <- matrix( c( 1, 2, 3, 4,
11, 22, 33, 44,
111, 222, 333, 444),
nrow=3,
ncol=4,
byrow=TRUE)
show(m_by_row)
# [,1] [,2] [,3] [,4]
# [1,] 1 2 3 4
# [2,] 11 22 33 44
# [3,] 111 222 333 444
n <- m_by_row[c(1,3,5,7)] # Note: counts as in a «by col» matrix.
show(n)
# [1] 1 111 22 3
# ------------------------------------------
# Create a 10x5 matrix with all
# cells being NA:
matrix(nrow=10, ncol=5)
# [,1] [,2] [,3] [,4] [,5]
# [1,] NA NA NA NA NA
# [2,] NA NA NA NA NA
# [3,] NA NA NA NA NA
# [4,] NA NA NA NA NA
# [5,] NA NA NA NA NA
# [6,] NA NA NA NA NA
# [7,] NA NA NA NA NA
# [8,] NA NA NA NA NA
# [9,] NA NA NA NA NA
# [10,] NA NA NA NA NA
# ------------------------------------------
is.matrix(m_by_col)
# [1] TRUE
dim(m_by_col)
# [1] 3 4
#
# See also
# -> colnames (to give names to the columns of the matrix)
#