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use REPL doctest for center/centered #254

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Aug 19, 2021
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use REPL doctest for center/centered #254

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5151d62
use REPL doctest for center/centered
johnnychen94 Aug 18, 2021
ca63d80
More clear explaination on `centered`
johnnychen94 Aug 19, 2021
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76 changes: 57 additions & 19 deletions src/OffsetArrays.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -672,16 +672,25 @@ a rounding procedure will be applied with mode `r`.
# Examples

```jldoctest; setup=:(using OffsetArrays)
A = reshape(collect(1:9), 3, 3)
c = OffsetArrays.center(A) # (2, 2)
A[c...] == 5 # true
julia> A = reshape(collect(1:9), 3, 3)
3×3 $(Matrix{Int}):
1 4 7
2 5 8
3 6 9

Ao = OffsetArray(A, -2, -2)
c = OffsetArrays.center(Ao) # (0, 0)
Ao[c...] == 5 # true
julia> c = OffsetArrays.center(A)
(2, 2)

# output
true
julia> A[c...]
5

julia> Ao = OffsetArray(A, -2, -2); # axes (-1:1, -1:1)

julia> c = OffsetArrays.center(Ao)
(0, 0)

julia> Ao[c...]
5
```

To shift the center coordinate of the given array to `(0, 0, ...)`, you
Expand All @@ -696,26 +705,55 @@ end
"""
centered(A, cp=center(A)) -> Ao

Shift the center coordinate of array `A` to `(0, 0, ...)`. If `size(A, k)`
is even, a rounding procedure will be applied with mode `r`.
Shift the center coordinate/point `cp` of array `A` to `(0, 0, ..., 0)`. Internally, this is
equivalent to `OffsetArray(A, .-cp)`.

!!! compat "OffsetArrays 1.9"
This method requires at least OffsetArrays 1.9.

# Examples

```jldoctest; setup=:(using OffsetArrays)
A = reshape(collect(1:9), 3, 3)
Ao = OffsetArrays.centered(A)
Ao[0, 0] == 5 # true
julia> A = reshape(collect(1:9), 3, 3)
3×3 $(Matrix{Int}):
1 4 7
2 5 8
3 6 9

julia> Ao = OffsetArrays.centered(A); # axes (-1:1, -1:1)

julia> Ao[0, 0]
5

julia> Ao = OffsetArray(A, OffsetArrays.Origin(0)); # axes (0:2, 0:2)

A = reshape(collect(1:9), 3, 3)
Ao = OffsetArray(A, OffsetArrays.Origin(0))
Aoo = OffsetArrays.centered(Ao)
Aoo[0, 0] == 5 # true
julia> Aoo = OffsetArrays.centered(Ao); # axes (-1:1, -1:1)

# output
true
julia> Aoo[0, 0]
5
```

Users are allowed to pass `cp` to change how "center point" is interpreted, but the meaning of the
output array should be reinterpreted as well. For instance, if `cp = map(last, axes(A))` then this
function no longer shifts the center point but instead the bottom-right point to `(0, 0, ..., 0)`.
A commonly usage of `cp` is to change the rounding behavior when the array is of even size at some
dimension:

```jldoctest; setup=:(using OffsetArrays)
julia> A = reshape(collect(1:4), 2, 2) # Ideally the center should be (1.5, 1.5) but OffsetArrays only support integer offsets
2×2 $(Matrix{Int}):
1 3
2 4

julia> OffsetArrays.centered(A, OffsetArrays.center(A, RoundUp)) # set (2, 2) as the center point
2×2 OffsetArray(::$(Matrix{Int}), -1:0, -1:0) with eltype $(Int) with indices -1:0×-1:0:
1 3
2 4

julia> OffsetArrays.centered(A, OffsetArrays.center(A, RoundDown)) # set (1, 1) as the center point
2×2 OffsetArray(::$(Matrix{Int}), 0:1, 0:1) with eltype $(Int) with indices 0:1×0:1:
1 3
2 4
```

See also [`center`](@ref OffsetArrays.center).
Expand Down