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improve a[...] .= handling of arrays of arrays and dicts of arrays #17568

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Jul 27, 2016
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improve a[...] .= handling of arrays of arrays and dicts of arrays #17568

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46ffc87
improve #17546 for a[...] .= handling of arrays of arrays and diction…
stevengj Jul 22, 2016
df4a58d
default dotview to getindex, using view only for AbstractArray
stevengj Jul 27, 2016
0eb3e3b
re-fix array-of-arrays case
stevengj Jul 27, 2016
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22 changes: 21 additions & 1 deletion base/broadcast.jl
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Expand Up @@ -5,7 +5,7 @@ module Broadcast
using Base.Cartesian
using Base: promote_op, promote_eltype, promote_eltype_op, @get!, _msk_end, unsafe_bitgetindex, linearindices, tail, OneTo, to_shape
import Base: .+, .-, .*, ./, .\, .//, .==, .<, .!=, .<=, .÷, .%, .<<, .>>, .^
export broadcast, broadcast!, bitbroadcast
export broadcast, broadcast!, bitbroadcast, dotview
export broadcast_getindex, broadcast_setindex!

## Broadcasting utilities ##
Expand Down Expand Up @@ -440,4 +440,24 @@ for (sigA, sigB) in ((BitArray, BitArray),
end
end

############################################################

# x[...] .= f.(y...) ---> broadcast!(f, dotview(x, ...), y...).
# The dotview function defaults to getindex, but we override it in
# a few cases to get the expected in-place behavior without affecting
# explicit calls to view. (All of this can go away if slices
# are changed to generate views by default.)

dotview(args...) = getindex(args...)
dotview(A::AbstractArray, args...) = view(A, args...)
dotview{T<:AbstractArray}(A::AbstractArray{T}, args...) = getindex(A, args...)
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@andreasnoack andreasnoack Feb 1, 2017 •
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@stevengj Why did you decide to default to getindex and not view in this case? @alanedelman showed me this example today

s = zeros(2,2) 
A = fill(s, 4, 4)
A[1:3,1:3] .= [ones(2,2)]

which doesn't set A because of this.

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You're right, it should be view also. I was thinking that view wasn't necessary, since A[i,j] returns a mutable object.

# avoid splatting penalty in common cases:
for nargs = 0:5
args = Symbol[Symbol("x",i) for i = 1:nargs]
eval(Expr(:(=), Expr(:call, :dotview, args...),
Expr(:call, :getindex, args...)))
eval(Expr(:(=), Expr(:call, :dotview, :(A::AbstractArray), args...),
Expr(:call, :view, :A, args...)))
end

end # module
2 changes: 1 addition & 1 deletion doc/manual/functions.rst
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Expand Up @@ -660,7 +660,7 @@ calls do not allocate new arrays over and over again for the results
except that, as above, the ``broadcast!`` loop is fused with any nested
"dot" calls. For example, ``X .= sin.(Y)`` is equivalent to
``broadcast!(sin, X, Y)``, overwriting ``X`` with ``sin.(Y)`` in-place.
If the left-hand side is a ``getindex`` expression, e.g.
If the left-hand side is an array-indexing expression, e.g.
``X[2:end] .= sin.(Y)``, then it translates to ``broadcast!`` on a ``view``,
e.g. ``broadcast!(sin, view(X, 2:endof(X)), Y)``, so that the left-hand
side is updated in-place.
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2 changes: 1 addition & 1 deletion src/julia-syntax.scm
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Expand Up @@ -1549,7 +1549,7 @@
(let* ((ex (partially-expand-ref expr))
(stmts (butlast (cdr ex)))
(refex (last (cdr ex)))
(nuref `(call (top view) ,(caddr refex) ,@(cdddr refex))))
(nuref `(call (top dotview) ,(caddr refex) ,@(cdddr refex))))
`(block ,@stmts ,nuref))
expr))

Expand Down
10 changes: 10 additions & 0 deletions test/broadcast.jl
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Expand Up @@ -274,6 +274,16 @@ let x = [1:4;], y = x
x[2:end] .= 1:3
@test y === x == [0,1,2,3]
end
let a = [[4, 5], [6, 7]]
a[1] .= 3
@test a == [[3, 3], [6, 7]]
end
let d = Dict(:foo => [1,3,7], (3,4) => [5,9])
d[:foo] .+= 2
@test d[:foo] == [3,5,9]
d[3,4] .-= 1
@test d[3,4] == [4,8]
end

# PR 16988
@test Base.promote_op(+, Bool) === Int
Expand Down