# Eachrow() error?

**URL:** <https://discourse.julialang.org/t/eachrow-error/64516>\
**Category:** New to Julia\
**Created:** [July 12, 2021, 3:48pm UTC](https://discourse.julialang.org/t/eachrow-error/64516 "2021-07-12T15:48:13Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![tomtom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomtom/32/5106_2.png) [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Post date:** [July 12, 2021, 3:48pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/1 "2021-07-12T15:48:13Z")

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```julia
julia> Random.seed!(1);
julia> x = randn(3, 5);
julia> x
3×5 Matrix{Float64}:
  0.297288 -0.0104452 2.29509 -2.26709 0.583708
  0.382396 -0.839027 0.408396 0.529966 0.963272
 -0.597634 0.311111 0.22901 0.431422 0.458791

julia> [maximum(eachrow(x)) [maximum(x[:, i]) for i in 1:5] ]
5×2 Matrix{Float64}:
  0.382396 0.382396
 -0.839027 0.311111
  0.408396 2.29509
  0.529966 0.529966
  0.963272 0.963272

```

the above example shows 2 problems:

1. some of the results not matched ???
2. it’s called “each **row** ” but it should be called “each **col** ” instead ???  
using v1.6.1. Thanks.

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<div class="post-metadata">

**Author:** ![tomtom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomtom/32/5106_2.png) [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Post date:** [July 12, 2021, 3:52pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/2 "2021-07-12T15:52:58Z")

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my misunderstanding. I should use `eachcol()` with **vectorized** `maximum()`:

```julia
julia> [maximum.(eachcol(x)) [maximum(x[:, i]) for i in 1:5] ]
5×2 Matrix{Float64}:
 0.382396 0.382396
 0.311111 0.311111
 2.29509 2.29509
 0.529966 0.529966
 0.963272 0.963272

```

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<div class="post-metadata">

**Author:** ![tomtom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomtom/32/5106_2.png) [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Post date:** [July 12, 2021, 4:07pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/3 "2021-07-12T16:07:24Z")

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In fact, the docs for `?eachcol` is _very confusing_:

```julia
Example
  ≡≡≡≡≡≡≡≡≡

  julia> a = [1 2; 3 4]
  2×2 Matrix{Int64}:
   1 2
   3 4
  
  julia> first(eachcol(a))
  2-element view(::Matrix{Int64}, :, 1) with eltype Int64:
   1
   3

```

reading the example above would be **confused** with the **naming** of `eachrow` vs `eachcol`. It also gives an **improper usage**!!

actually the example should be provided as:

```julia
julia> a = [1 2; 3 4]
2×2 Matrix{Int64}:
 1 2
 3 4

julia> first.(eachcol(a))
2-element Vector{Int64}:
 1
 2

```

hope it helps.

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<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [July 12, 2021, 4:11pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/4 "2021-07-12T16:11:40Z")

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Think of `eachrow` and `eachcol` as `Vector`s of `Vector`s. `first(eachcol(a))` just gives the first column. I think the docs are pretty understandable.

Maybe part of the confusion is `maximum` on `Vector` of `Vector`s. Julia compares vectors elementwise, so that `[1, 100] > [1, 2]` (I always forget the name for this)

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**Author:** ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)\
**Post date:** [July 12, 2021, 4:11pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/5 "2021-07-12T16:11:50Z")

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> [@tomtom](#):
>
> `maximum(x[:, i])`

isn’t that a column? it shouldn’t match what eachrow gives you right?

```julia
2×2 Matrix{Int64}:
 1 2
 3 4

```

1 and 3 form a column, are you from a culture that calls that a row? Eachcol gives you a collection, think of it as `[col1, col2]`, so when you call `first()`, you’re getting the first column, `col1`, which is 1 and 3 in the above example.

On the other hand, calling `first.()` is getting first element of EACH of the columns, of course you get the first row then.

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<div class="post-metadata">

**Author:** ![tomtom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomtom/32/5106_2.png) [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Post date:** [July 12, 2021, 5:00pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/6 "2021-07-12T17:00:45Z")

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> [@pdeffebach](#):
>
> Maybe part of the confusion is `maximum` on `Vector` of `Vector` s

yes. If we replace `first()` with `maximum()` in the docs example, my concern would be apparent.

I think at least we should **include** the use of `first.()` in the docs example for clarification and comparison.

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<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [July 12, 2021, 5:01pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/7 "2021-07-12T17:01:52Z")

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Feel free to make a PR, then, to improve the docs.

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<div class="post-metadata">

**Author:** ![mcabbott](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mcabbott/32/6603_2.png) [@mcabbott](https://discourse.julialang.org/u/mcabbott)\
**Post date:** [July 12, 2021, 5:03pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/8 "2021-07-12T17:03:18Z")

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If you add something to the docs, it should probably be `map(first, eachcol(a))`. Broadcasting over the generator collects it first, which isn’t necessary.

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<div class="post-metadata">

**Author:** ![tomtom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomtom/32/5106_2.png) [@tomtom](https://discourse.julialang.org/u/tomtom)\
**Post date:** [July 12, 2021, 5:15pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/9 "2021-07-12T17:15:06Z")

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> [@pdeffebach](#):
>
> Feel free to make a PR, then, to improve the docs.

I want to do so… but I just don’t know how… it says “You must be on a branch to propose or make changes to this file”… what could I do? How to be “on” a branch???

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<div class="post-metadata">

**Author:** ![mcabbott](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mcabbott/32/6603_2.png) [@mcabbott](https://discourse.julialang.org/u/mcabbott)\
**Post date:** [July 12, 2021, 5:27pm UTC](https://discourse.julialang.org/t/eachrow-error/64516/10 "2021-07-12T17:27:12Z")

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>
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