# A question about array

**URL:** <https://discourse.julialang.org/t/a-question-about-array/37828>\
**Category:** Optimization (Mathematical)\
**Tags:** question\
**Created:** [April 19, 2020, 2:04am UTC](https://discourse.julialang.org/t/a-question-about-array/37828 "2020-04-19T02:04:24Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![abcde](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/abcde/32/16180_2.png) [@abcde](https://discourse.julialang.org/u/abcde)\
**Post date:** [April 19, 2020, 2:04am UTC](https://discourse.julialang.org/t/a-question-about-array/37828/1 "2020-04-19T02:04:24Z")

</div>

```julia
a=[7 -1 -1]
b=union(a)
c=reshape(b,(:,3))
print(c)

```

this is a simple code,but it is wrong,it shows:  
DimensionMismatch(“array size 2 must be divisible by the product of the new dimensions (Colon(), 3)”)  
why?thank you!

---

<div class="post-metadata">

**Author:** ![L\_Adam](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/l_adam/32/12086_2.png) [@L\_Adam](https://discourse.julialang.org/u/L_Adam)\
**Post date:** [April 19, 2020, 2:32am UTC](https://discourse.julialang.org/t/a-question-about-array/37828/2 "2020-04-19T02:32:04Z")

</div>

```julia
julia> a = [7 -1 -1]
1×3 Array{Int64,2}:
 7 -1 -1

julia> union(a)
2-element Array{Int64,1}:
  7
 -1

```

There are only 2 elements