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Pattern Sequence-based stride

Source: R/stride_ptrn.R
stride_ptrn.Rd

stride_ptrn() specifies a patterned sequence, in the form of (start:end)[ptrn], for use in the long_ methods.

For example:
the sub-set operation long_x(x, stride_ptrn(start, end, ptrn))
is conceptually equivalent to
x[(start:end)[ptrn]]

ptrn_len(start, end, ptrn) calculates the length of (start:end)[ptrn], without actually allocating said vector.

Usage

stride_ptrn(start, end, ptrn)

ptrn_len(start, end, ptrn)

Arguments

start

natural scalar giving the starting point of the sequence.

end

natural scalar giving the ending point of the sequence.

ptrn

a logical vector, giving the pattern.
ptrn must contain at least 1 TRUE and 1 FALSE element, to avoid ambiguity.
ptrn must have length that fulfils all of the following conditions:

  • it is >= 2

  • it is <= length(start:end)

  • it is <= 2^31 - 1

Value

An object of class "stride".

See also

squarebrackets_stride

Examples



x <- mutatomic(1:1e7)

long_x(x, stride_ptrn(2, 20, c(TRUE, FALSE, FALSE, TRUE)))
#> [1]  2  5  6  9 10 13 14 17 18
#> mutatomic 
#> typeof:  integer 

long_x(x, stride_ptrn(20, 2, c(TRUE, FALSE, FALSE, TRUE)))
#> [1] 20 17 16 13 12  9  8  5  4
#> mutatomic 
#> typeof:  integer 

long_x(x, stride_ptrn(2, 20, c(TRUE, FALSE, FALSE, TRUE)), -1) |> head()
#> [1]  1  3  4  7  8 11
#> mutatomic 
#> typeof:  integer 

long_x(x, stride_ptrn(20, 2, c(TRUE, FALSE, FALSE, TRUE)), -1) |> head()
#> [1]  1  2  3  6  7 10
#> mutatomic 
#> typeof:  integer