findp

[John Myles White]

Having just recently discovered anyp() and allp() in Base, I wrote a complementary function called findp(). It seems like it would be generally useful, but I'm hesitant to propose adding more things to Base. As such, I'm just leaving it below in case others have a sense for where we might want to put it:

function findp(p::Function, a::AbstractArray)
n = length(a)
indices = Array(Int, n)
t = 0
for i in 1:n
if p(a[i])
t += 1
indices[t] = i
end
end
return indices[1:t]
end

findp(iseven, [1, 2, 3, 4, 5])

[Harlan Harris]

I think find(f, array) will do the same thing. See https://github.com/JuliaLang/julia/blob/master/base/array.jl, around line 1150 for variations...

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[John Myles White]

Ah. I just assumed that wouldn't exist because anyp() and allp() exist.

 -- John

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[Glen Hertz]

Hi,

I would make the same assumption...

I wrote my own `find` because I couldn't find `find`.  I was looking for a function starting with 'ind' or named 'indices' .  Calling a function `find` that returns indices seems too generic to me.  But now I know about it.  

Glen

[Harlan Harris]

It's a Matlab thing...

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[Diego Javier Zea]

Looking into countp() [ https://groups.google.com/forum/#!topic/julia-dev/R_gMPWNvFYU ] looks like the predicate is not in-lined on the function.
The inline version of the predicate is more than 13x faster than using countp() and a lambda function, and scales better than the function in base.
Maybe can be the same with find() ?

[John Myles White]

Can I propose that we start producing a Julia Rosetta Stone that can be indexed for searching the language?

Here's a one-row database that translates find into a few languages:

https://docs.google.com/spreadsheet/ccc?key=0Ai9cmDERDCGgdGlpeHRGcUlQejFGalFxS2RNdjlOV1E

We already have a much more complete spreadsheet for statistical functions:

https://docs.google.com/spreadsheet/ccc?key=0Ai9cmDERDCGgdDJ6VDQtQjBGWm5LTzh6R0lRNHY1RVE

 -- John

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