# Advantages of explicitly using "map" or "broadcast" wrappers?

**URL:** <https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371>\
**Category:** Internals & Design\
**Tags:** question\
**Created:** [December 20, 2021, 2:47pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371 "2021-12-20T14:47:17Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [December 20, 2021, 2:47pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/1 "2021-12-20T14:47:17Z")

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For example, if I have four vectors A, B, C, and D, and my goal is to find the index of the rows with A\>-10, B\>15, C\>500 and D\>200.

In Matlab I can achieve that by doing the below:  
`Index1 = A>-10 && B>15 && C>500 && D>200`

In comparison, I would have to write a more complex syntax in Julia as below:

```julia
Index1 = map(A, B, C, D) do a,b,c,d
        a>-10 && b>=15 && c>500 && d>200
end

```

I’m wondering why Julia is making it so complex? what is the advantage of doing it this way?

Thanks!

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**Author:** ![giordano](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/giordano/32/2166_2.png) [@giordano](https://discourse.julialang.org/u/giordano)\
**Post date:** [December 20, 2021, 2:50pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/2 "2021-12-20T14:50:06Z")

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Wouldn’t explicit broadcast

```julia
julia> A = 1000randn(10); B = 1000randn(10); C = 1000randn(10); D = 1000randn(10);

julia> mask = @. A > -10 && B > 15 && C > 500 && D > 200
10-element BitVector:
 0
 0
 0
 0
 0
 1
 0
 0
 0
 0

```

work as well?

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**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [December 20, 2021, 2:52pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/3 "2021-12-20T14:52:39Z")

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Many thanks! As a former Matlab user, I find this one easier to understand.

It’s a bonus to learn of the `@.` thing 👍

---

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**Author:** ![antoine-levitt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/antoine-levitt/32/4008_2.png) [@antoine-levitt](https://discourse.julialang.org/u/antoine-levitt)\
**Post date:** [December 20, 2021, 2:54pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/4 "2021-12-20T14:54:56Z")

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(also note that in matlab this kind of array masks is necessary to get not-crappy performance, but in julia it is often faster to just write out the for loop. Whether that is more or less clear than masks depends on the context)

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**Author:** ![Seif\_Shebl](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Seif\_Shebl](https://discourse.julialang.org/u/Seif_Shebl)\
**Post date:** [December 20, 2021, 9:29pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/5 "2021-12-20T21:29:57Z")

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You can do the same in Julia, and as a bonus, it is faster even in this vectorized form. But if you want to up your game, you can get it 4X faster in Julia with 4X less memory by writing a one-liner loop:

```julia
A, B, C, D = [1000randn(1000) for i=1:4]

using BenchmarkTools
@btime out = @. ($A > -10) & ($B > 15) & ($C > 500) & ($D > 200)
  2.556 μs (3 allocations: 4.41 KiB)

@btime [($A[i]>-10) & ($B[i]>15) & ($C[i]>500) & ($D[i]>200) for i=1:length($A)]
  775.962 ns (1 allocation: 1.06 KiB)

```

In MATLAB, for comparison:

```julia
A = 1000*randn(1000,1);  
B = 1000*randn(1000,1);  
C = 1000*randn(1000,1);  
D = 1000*randn(1000,1);

out = @() (A > -10) & (B > 15) & (C > 500) & (D > 200);
timeit(out)

ans =

   3.1057e-06

```

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<div class="post-metadata">

**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [December 20, 2021, 9:57pm UTC](https://discourse.julialang.org/t/advantages-of-explicitly-using-map-or-broadcast-wrappers/73371/6 "2021-12-20T21:57:29Z")

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Many thanks!

This thread is becoming very interesting. There are so many way of writing this code cleanly and fast!

Julia is truly amazing.