implement map for multiple array arguments

[zingales]

i skimmed the other map thread and felt that this was off topic enough and not as important, so i decided to start another thread (even though they talk about the same function)

if the function has 1 argument then its done simply like so

julia> map(char, [1,2,3,4])
['\x01','\x02','\x03','\x04']

however if the requires multiple arguments this has to be done with an array of arrays

julia> map(x->is(x[1],x[2]), {{2,3},{3,4},{4,5}})
{6,12,20}

this is inconsistency could be fixed, by forcing even the 1-dimensional case also require a array of arrays. This however, would seem to make the matters of calling this function worse. But would be entirely consistent

i feel the optimal solution, is that if the function being passed has a predefined number of arguments, that it automatically set picks out that number of arguments from array, and only if the function usess the ... must u pass it an array of arrays

exmaple:

julia> function threenumadd(num1,num2,num3)
    num1+num2+num3
end

julia> map(threenumadd, [1,2,3,4,5,6])
[6,15]

julia> map(+, {{1,2},{3,4},{5,6}})
[3,7,11]

[JeffBezanson]

It's well-established that to call map on an N-argument function, you pass N lists (or whatever collection) to map:

julia> map(+, (1,2), (3,4))
(4,6)

The N-argument case isn't currently implemented for arrays though.

[JeffBezanson]

Also, this:

julia> map(x->is(x[1],x[2]), {{2,3},{3,4},{4,5}})
{6,12,20}

is not an inconsistency by any stretch of the imagination. The "problem" here is consistency: map on one array calls a function of one argument on each element of the array, period. x->is(x[1],x[2]) is a perfectly ordinary one-argument function. In fact this case illustrates why you could not have special behavior for an array of arrays: the mapped function might take an array as its argument, so it would be ambiguous whether the function should be called on whole arrays or their elements as N arguments.

[zingales]

oooooOOOOOOoOOOOOOOoooo i didn't know you could do that. I completely revoke
my previous statement.

Giuseppe

On Mon, Aug 15, 2011 at 9:06 PM, JeffBezanson <
[email protected]>wrote:

Also, this:

julia> map(x->is(x[1],x[2]), {{2,3},{3,4},{4,5}})
{6,12,20}

is not an inconsistency by any stretch of the imagination. The "problem"
here is consistency: map on one array calls a function of one argument on
each element of the array, period. x->is(x[1],x[2]) is a perfectly
ordinary one-argument function. In fact this case illustrates why you could
not have special behavior for an array of arrays: the mapped function
might take an array as its argument, so it would be ambiguous whether the
function should be called on whole arrays or their elements as N arguments.

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