# Jldoctest: number of elements printed for array
**URL:** https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794
**Category:** General Usage
**Tags:** documentation
**Created:** [May 3, 2024, 1:42pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794 "2024-05-03T13:42:19Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 1:42pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/1 "2024-05-03T13:42:19Z")
In a docstring like:
````julia-repl
```jldoctest
julia> x = rand(1000)
1000-element Vector{Float64}:
0.9193285028224774
0.35444797029663266
0.1201916693868853
0.35371426411293694
0.11668489865605236
0.6506991967008628
⋮
0.5180636146804571
0.3354691171077989
0.046577899510561904
0.5993088546568675
0.3926367429008284
0.7955460631376658
```#
````
Is there a way to set the number of elements of the array to be printed or tested? Or make the test not fail if the output has fewer or more elements than what is printed (assuming that
the first and last elements match)?
This is the kind of output I’m talking about:
```julia
│ Expected output:
│
│ 584-element Vector{Tuple{Int64, Int64, Float64}}:
│ (1, 12, 7.360804915224965)
│ (1, 13, 7.017762962654125)
│ ⋮
│ (50, 37, 7.546490310071297)
│ (50, 39, 3.900154099519657)
│
│ diff =
│ 584-element Vector{Tuple{Int64, Int64, Float64}}:
│ (1, 12, 7.360804915224965)
│ (1, 13, 7.017762962654125)
│ (1, 24, 7.976895636774997)
│ (1, 29, 3.177028328485598)
│ (1, 44, 5.394713986857875)
│ (1, 45, 5.4248765884580274)
│ (1, 11, 4.088651856052312)
│ (1, 17, 5.93977280710298)
│ (1, 30, 2.457228927063981)
│ (1, 28, 6.853834401267658)
│ ⋮
│ (50, 3, 7.232267901564487)
│ (50, 10, 3.9736202636890203)
│ (50, 27, 6.257296620746054)
│ (50, 32, 3.1099665593057426)
│ (50, 33, 2.919291694915052)
│ (50, 35, 5.043227240567294)
│ (50, 20, 6.995405134800987)
│ (50, 37, 7.546490310071297)
│ (50, 39, 3.900154099519657)
└ @ Documenter ~/.julia/dev/CellListMap/src/neighborlists.jl:568
```
(these tests fail because of the number of elements, the floating point precision is being filtered out).
20 elements, as it is expected, is too much, makes reading the docstring cumbersome.
---
### Author:  [@aryavorskiy](https://discourse.julialang.org/u/aryavorskiy)
#### Post date: [May 3, 2024, 7:21pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/2 "2024-05-03T19:21:13Z")
Hi!
Probably [doctest filtering](https://documenter.juliadocs.org/stable/man/doctests/#Filtering-Doctests) is what you need. Basically, you define a regular expression that gets replaced both on expected and evaluated inputs, and after that they are compared.
In your case `filter = r"(.*)\n(.*)\n(.*)\n[.\n]*(.*)\n(.*)" => s"\1\n\2\n\3\n\4\n\5\n"` might do the thing (keep 3 first and 2 last lines, ignore all that remains; you might need some more regex trickery here).
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 7:48pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/3 "2024-05-03T19:48:14Z")
I which we could (can we?) pass general functions to filter the results. Regex trickery is definitely not my thing, and I just get stuck even with the simpler things.
(and it seems not be the thing of chatgpt either, it has failed so far for me in this one).
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [May 3, 2024, 8:01pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/4 "2024-05-03T20:01:52Z")
> [@lmiq](#):
>
> Is there a way to set the number of elements of the array to be printed or tested?
In a [`@meta` setup block](https://documenter.juliadocs.org/stable/man/doctests/#Setup-Code) you should be able to control this by setting the `displaysize` option, e.g.:
```jl
julia> Base.active_repl.options.iocontext[:displaysize] = (10,80);
julia> [1:1000;]
1000-element Vector{Int64}:
1
2
3
⋮
999
1000
julia> Base.active_repl.options.iocontext[:displaysize] = (5,80);
julia> [1:1000;]
1000-element Vector{Int64}:
⋮
```
assuming Documenter.jl uses `Base.active_repl`’s display, or there is some other way to control the `IOContext` that it uses.
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 8:05pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/5 "2024-05-03T20:05:58Z")
Unfortunately it seems to ignore that. I’ve tried it.
Also, I’m willing to have that in docstrings, so I’m not sure those meta blocks will be considered when the user is just navigating the `help>` entries.
---
### Author:  [@kimikage](https://discourse.julialang.org/u/kimikage)
#### Post date: [May 3, 2024, 9:04pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/6 "2024-05-03T21:04:30Z")
I understand the motivation behind this, but in the first place, the doctest is to ensure that the documentation matches the actual results.
If you don’t want to show (and check) some data, shouldn’t you write such example codes?
I mean:
```julia-repl
julia> x[end-1:end] # The last two elements indicate the ...
2-element Vector{Float64}:
0.3926367429008284
0.7955460631376658
```
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 10:12pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/7 "2024-05-03T22:12:30Z")
Doc tests are the only place where I can test `show` methods with ease. Also, they are checked for consistency, and don’t become outdated, as example codes do. This is why having them, even if somehow filtered, is better than having example codes.
Also, the number of output lines of an array is an arbitrary parameter of the current display section, in some sense I think that the default behavior of doc tests should be matching what is displayed in the test, not any specific number of lines.
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 10:14pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/8 "2024-05-03T22:14:24Z")
> [@kimikage](#):
>
> `x[end-1:end`
That specifically does not interest me, because the number of elements of the a array is a meaningful parameter. (and I don’t want an example to artificially slice or compute the length of the output).
---
### Author:  [@kimikage](https://discourse.julialang.org/u/kimikage)
#### Post date: [May 3, 2024, 10:44pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/9 "2024-05-03T22:44:21Z")
> [@lmiq](#):
>
> Doc tests are the only place where I can test `show` methods with ease.
This is off-topic, but if you are customizing `show` (or `print`), you should write explicit tests for it. That may be tedious (since different versions of julia have different styles, such as whether to include spaces, use aliases, etc.), but not difficult.
> [@lmiq](#):
>
> That specifically does not interest me
You noted that it makes sense to show the last element. If it has no value to the user (not you), there is no need to indicate it.
```julia-repl
julia> summary(x)
"1000-element Vector{Float64}"
```
---
### Author:  [@kimikage](https://discourse.julialang.org/u/kimikage)
#### Post date: [May 3, 2024, 11:01pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/10 "2024-05-03T23:01:55Z")
> [@lmiq](#):
>
> I’m not sure those meta blocks will be considered when the user is just navigating the `help>` entries.
There is also the [block-level-setup-code](https://documenter.juliadocs.org/stable/man/doctests/#Block-level-setup-code). Many docstrings use it and unfortunately we have to accept its redundancy (for now).
I do not know how to change the IO context.
In the first place, there is basically no functionality for docstrings to change with the user context. There are a few tricky ways, but they are more tricky than the Regex stuff.
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 3, 2024, 11:08pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/11 "2024-05-03T23:08:01Z")
> [@kimikage](#):
>
> `julia> summary(x)`
That, or suggesting to call length, in an example, defeats the purpose of the example. It should just look as something the user will actually do.
> [@kimikage](#):
>
> This is off-topic, but if you are customizing `show` (or `print`), you should write explicit tests for it.
Exactly that, but it would be a waste of time to write all the machinery to check the output of a show method to _not_ use it in doc tests. That’s exactly why I would like to provide custom functions to the filter option. It would be a gain-gain situation.
---
### Author:  [@kimikage](https://discourse.julialang.org/u/kimikage)
#### Post date: [May 3, 2024, 11:32pm UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/12 "2024-05-03T23:32:11Z")
> [@lmiq](#):
>
> It should just look as something the user will actually do.
I prefer examples to be minimalistic, which is easier to understand, than to be practical.
For example, pitfalls should be shown in examples, but that does not mean that the document writer wants the user to _actually_ fall into the pitfalls.
If there is a wide gap between the simplicity and practicality, a practical tutorial article or notebook would be better.
This is a matter of values, not a discussion here.
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [May 4, 2024, 12:06am UTC](https://discourse.julialang.org/t/jldoctest-number-of-elements-printed-for-array/113794/13 "2024-05-04T00:06:21Z")
> [@kimikage](#):
>
> I do not know how to change the IO context.
There is an open issue: [Controlling output text width in doctests · Issue #942 · JuliaDocs/Documenter.jl · GitHub](https://github.com/JuliaDocs/Documenter.jl/issues/942) — sounds like you can maybe use the `LINES` environment variable in `docs/make.jl`.