idx_r() computes integer index range(s).
Arguments
- x
the object for which to compute subset indices.
- m, from, to, by
see cp_seq.
Value
If length(m) == 1L: a vector of numeric indices.
If length(m) > 1L: a list of the same length as m,
containing numeric vectors of indices.
Examples
x <- data.frame(
a = 1:10, b = letters[1:10], c = factor(letters[1:10]), d = -1:-10
)
print(x)
#> a b c d
#> 1 1 a a -1
#> 2 2 b b -2
#> 3 3 c c -3
#> 4 4 d d -4
#> 5 5 e e -5
#> 6 6 f f -6
#> 7 7 g g -7
#> 8 8 h h -8
#> 9 9 i i -9
#> 10 10 j j -10
ind1 <- idx_r(x, 1, 2, 2* -1i) # rows 2:(nrow(x)-1)
sb2_x(x, ind1) # extract the row range
#> a b c d
#> 1 2 b b -2
#> 2 3 c c -3
#> 3 4 d d -4
#> 4 5 e e -5
#> 5 6 f f -6
#> 6 7 g g -7
#> 7 8 h h -8
#> 8 9 i i -9
x <- array(1:125, c(5,5,5))
dims <- 1:3
sub <- idx_r(x, dims, 2, 2* -1i) # 2:(n-1) for every dimension
sb_x(x, sub, dims) # same as x[ 2:4, 2:4, 2:4, drop = FALSE]
#> , , 1
#>
#> [,1] [,2] [,3]
#> [1,] 32 37 42
#> [2,] 33 38 43
#> [3,] 34 39 44
#>
#> , , 2
#>
#> [,1] [,2] [,3]
#> [1,] 57 62 67
#> [2,] 58 63 68
#> [3,] 59 64 69
#>
#> , , 3
#>
#> [,1] [,2] [,3]
#> [1,] 82 87 92
#> [2,] 83 88 93
#> [3,] 84 89 94
#>
x <- letters
x[idx_r(x, 0, 2, 2* -1i)]
#> [1] "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t"
#> [20] "u" "v" "w" "x" "y"