# \[Plots\] Efficient scatter plot of a 2×N Array
**URL:** https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803
**Category:** Visualization
**Tags:** question, plotting, array
**Created:** [December 3, 2019, 2:10pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803 "2019-12-03T14:10:06Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@4aHxKzD](https://discourse.julialang.org/u/4aHxKzD)
#### Post date: [December 3, 2019, 2:10pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/1 "2019-12-03T14:10:06Z")
When we want to plot a series of points we simply write:
```julia
points = rand(10000)
scatter(points)
```
this assumes a `y = rand(10000)` and ` x = 1:10000`. From the [Official documentation - Argument Passing Behavior](https://docs.julialang.org/en/v1/manual/functions/#Argument-Passing-Behavior-1)
> Julia function arguments follow a convention sometimes called “pass-by-sharing”, which means that values are not copied when they are passed to functions.
I know that in this case the variable `points` is not copied when passed to `scatter`.
Now consider having a 2×500 Array of points, i.e., 500 points in a 2D space. For this case, the scatter plot requires you to pass both x and y series separately. We usually do this by writing
```julia
scatter(points[1, :], points[2, :])
```
In this case `points[1, :]` and `points[2, :]` are copies of each row of `points` that are created before being passed to the function. A way to prevent this is
```julia
scatter(view(points, 1, :), view(points, 2, :))
```
but it is a bit verbose, is there a way to achieve the same behavior without calling view?
---
### Author:  [@tkluck](https://discourse.julialang.org/u/tkluck)
#### Post date: [December 3, 2019, 2:59pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/2 "2019-12-03T14:59:35Z")
> [@4aHxKzD](#):
>
> A way to prevent this is
>
> ```julia
> scatter(view(points, 1, :), view(points, 2, :))
>
> ```
>
> but it is a bit verbose, is there a way to achieve the same behavior without calling view?
This still calls `view` but is already less verbose:
```julia
@views scatter(points[1,:], points[2,:])
```
---
### Author:  [@improbable22](https://discourse.julialang.org/u/improbable22)
#### Post date: [December 3, 2019, 3:06pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/3 "2019-12-03T15:06:12Z")
You can also write `scatter(eachrow(points)...)`, which is the same views but a bit shorter.
---
### Author:  [@yha](https://discourse.julialang.org/u/yha)
#### Post date: [December 3, 2019, 3:07pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/4 "2019-12-03T15:07:20Z")
Did you benchmark this?
I doubt that the copying would take any noticeable amount of time with a 2x500 array, compared the plotting (and I suspect if the array is actually large enough for this to matter, you want a 2d histogram rather than a scatter plot).
---
### Author:  [@4aHxKzD](https://discourse.julialang.org/u/4aHxKzD)
#### Post date: [December 3, 2019, 4:33pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/5 "2019-12-03T16:33:11Z")
I used 500 for the sake of example, but yes in practice it might not be relevant. I asked out of curiosity and still managed to learn one or two things from the answers.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [December 3, 2019, 5:26pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/6 "2019-12-03T17:26:15Z")
It is very likely that plotting time will also scale at least linearly or worse (when a render has to figure out overlap in case of overplotting) with the number of points.
Also, [Performance Tips · The Julia Language](https://docs.julialang.org/en/v1/manual/performance-tips/#Copying-data-is-not-always-bad-1) .
The key to efficient Julia code is to be aware of various performance pitfalls and optimization techniques, then benchmark and profile, and apply them _where needed_.
---
### Author:  [@mkborregaard](https://discourse.julialang.org/u/mkborregaard)
#### Post date: [December 3, 2019, 11:24pm UTC](https://discourse.julialang.org/t/plots-efficient-scatter-plot-of-a-2xn-array/31803/7 "2019-12-03T23:24:58Z")
One of the first things Plots does is - copy the input. So copying manually first should introduce a constant but quite small time increase.