# How to delete the number of lines plotted in the graph

**URL:** <https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541>\
**Category:** New to Julia\
**Tags:** question, plotting\
**Created:** [January 8, 2024, 10:40pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541 "2024-01-08T22:40:32Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![kim1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kim1/32/205937_2.png) [@kim1](https://discourse.julialang.org/u/kim1)\
**Post date:** [January 8, 2024, 10:40pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/1 "2024-01-08T22:40:32Z")

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Hi guys Im trying to plot my graph but it keep on increasing the number of line plotted each time. Plot{Plots.GRBackend() n=5} I want only n=2. How do I delete the unnecessary lines.

 ![plot_39_page-0001](https://global.discourse-cdn.com/julialang/original/3X/6/a/6a028460a9321a82477390899f050b1ea39c643f.jpeg)

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**Author:** ![mike.ingold](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike.ingold/32/203749_2.png) [@mike.ingold](https://discourse.julialang.org/u/mike.ingold)\
**Post date:** [January 9, 2024, 1:19am UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/2 "2024-01-09T01:19:30Z")

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Do you have a code snippet that you’re using to generate this?

Ref: [Please read: make it easier to help you](https://discourse.julialang.org/t/please-read-make-it-easier-to-help-you/14757)

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<div class="post-metadata">

**Author:** ![kim1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kim1/32/205937_2.png) [@kim1](https://discourse.julialang.org/u/kim1)\
**Post date:** [January 9, 2024, 2:37pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/3 "2024-01-09T14:37:21Z")

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Here is the code I’m currently using

```julia
    function f(x; θ=15*pi/180)
        if (x>-R1*sin(θ)) && (x<R1*sin(θ))
            (R_throat+R1*(1-cos(asin(x/R1))))
        elseif (x>-R1*sind(θ))
            (m*x+Y0)
        end
    end

    using Plots

    x=range(0, Xe, length=100)
    y=m .* x .+Y0
    plot((x,f.(x, θ=15*pi/180)), ylims=(0,0.75), color="blue")
    plot!((-x,f.(x, θ=15*pi/180)), ylims=(0,0.75), color="blue")

```

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<div class="post-metadata">

**Author:** ![mike.ingold](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike.ingold/32/203749_2.png) [@mike.ingold](https://discourse.julialang.org/u/mike.ingold)\
**Post date:** [January 9, 2024, 3:40pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/4 "2024-01-09T15:40:45Z")

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I’m not sure of your experience level with the language, so pardon if some are pedantic, but I’ve got a couple of notes here that I hope might be helpful.

Your function `f` has inconsistent usage of `sin` vs `sind`; I think under the `elseif` condition you intended to use `sin(θ)`. Also, the `if`/`elseif` conditions you provided can be cleaned up a bit. What happens if `x == R1*sin(θ)`? See the code block at the bottom of this post for a suggestion.

You’re referencing a few global variables that aren’t provided, and I can’t replicate your current result as-is. Specifically, `R1`, `R_throat`, `m`, `Y0`, and `Xe` aren’t defined here. In some cases, like in the REPL, Julia will run this function without issue; but in others like executing a source file directly you can get errors/warnings when trying to access globally-scoped variables from within a function without explicitly declaring them as global. Referencing globals from within a function has some drawbacks, especially in terms of performance, but sometimes it’s what you want to do.

You define a function `f(x; θ=15*pi/180)` which has a [keyword argument](https://docs.julialang.org/en/v1/manual/functions/#Keyword-Arguments) θ with a default value `15pi/180`. This means that any time you call simply `f(x)`, it will by default have defined a variable `θ = 15pi/180` inside. So, in your plot calls at the bottom there’s no real need to call `f.(x, θ=15*pi/180))` since that’s already the default value; you could also just have written `f.(x)` here.

The Plots.jl package always felt slightly cryptic to me, so I’m not sure if putting your data in a tuple, i.e. `(x, y)` has any special meaning, but the syntax `plot(x, y)` where `x` and `y` are equal-length vectors of corresponding point values works just fine.

Keyword argument settings passed to `plot` are usually respected when the figure is modified by a `plot!` call, so no need to repeat the `ylims` settings. In fact, you can also make a `plot!` call with nothing but keyword arguments if you’d like to group those settings all at once.

```julia
using Plots

# Values of these globals not provided, so I'm just guessing for each
m = 0.2
R1 = 5.0
R_throat = 0.25
Xe = pi/2
Y0 = 0.25

function f(x; θ=15pi/180)
    # These names reference global-scope variables (defined above)
    global Y0, R1, R_throat, m

    if -R1*sin(θ) < x < R1*sin(θ)
        return R_throat + R1 * (1 - cos(asin(x/R1)))
    else
        return m * x + Y0
    end
end

# Plot f over a range of x's
xs = range(0, Xe, length=100)
plot(xs, f.(xs), color=:blue)
plot!(-xs, f.(xs), color=:red)
plot!(ylims=(0,0.75), legend=:bottomright)

```

![image](https://global.discourse-cdn.com/julialang/original/3X/8/5/855bcc25fb9768ddf548f7d2f554b5f0c8005ea9.png)

Or, alternately, the plot could be constructed as:

```julia
xs = range(-Xe, Xe, length=100)
plot(xs, f.(abs.(xs)), color=:blue)
plot!(ylims=(0,0.75), legend=:bottomright)

```

![image](https://global.discourse-cdn.com/julialang/original/3X/f/1/f15c50ff0dada4abf0f4e504dba585b17e261fbb.png)

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<div class="post-metadata">

**Author:** ![kim1](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kim1/32/205937_2.png) [@kim1](https://discourse.julialang.org/u/kim1)\
**Post date:** [January 9, 2024, 4:45pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/5 "2024-01-09T16:45:25Z")

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Thank you very much I like your method and its much more nicer, now I gotta do the same thing as I did before but mirror it to the y axis been trying to do this method for a few days now 😍. And its kinda weird but your method does not occur the problem that I had faced before which is [this](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541) what does legend=: bottomright do if I may ask?

```julia
using Plots

function f(x; θ=15pi/180)
    
    global Y0, R1, R_throat, m

    if -R1*sin(θ) < x < R1*sin(θ)
        return R_throat + R1 * (1 - cos(asin(x/R1)))
    else
        return m * x + Y0
    end
end

x = range(0, Xe, length=100)
plot(x, f.(x), color=:blue)
plot!(x, -f.(x), color=:blue)
plot!(ylims=(-0.75,0.75), legend=:bottomright)
title!("Rocket Nozzle")
xlabel!("m")
ylabel!("Radius(m)")

```

 ![plot_60_page-0001](https://global.discourse-cdn.com/julialang/original/3X/5/0/50e77e5e719ca45e5a7fda56bd75c69ea2fc9d22.jpeg)

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<div class="post-metadata">

**Author:** ![mike.ingold](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike.ingold/32/203749_2.png) [@mike.ingold](https://discourse.julialang.org/u/mike.ingold)\
**Post date:** [January 9, 2024, 4:56pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/6 "2024-01-09T16:56:40Z")

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Plots.jl has a [keyword setting for subplots](https://docs.juliaplots.org/stable/generated/attributes_subplot/) `legend_position`, which can be set using the shorter alias `legend`, that requests it place the plot legend (the box with the line labels `y1` and `y2` in your example) in a specific location. Without the setting, Plots will just select what it thinks is a suitable location, but sometimes it’s nice to put it where you want it instead.

You can also control the labels used to describe the lines in the legend by adding a `label` keyword when the particular line is plotted.

```julia
plot(x, f.(x), color=:blue, label="The top line")
plot!(x, -f.(x), color=:blue, label="The bottom line")

```

Alternatively, `label=missing` indicates that you don’t want that particular line to be labeled in a legend.

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<div class="post-metadata">

**Author:** ![mike.ingold](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike.ingold/32/203749_2.png) [@mike.ingold](https://discourse.julialang.org/u/mike.ingold)\
**Post date:** [January 9, 2024, 5:01pm UTC](https://discourse.julialang.org/t/how-to-delete-the-number-of-lines-plotted-in-the-graph/108541/7 "2024-01-09T17:01:40Z")

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> [@kim1](#):
>
> And its kinda weird but your method does not occur the problem that I had faced before

I suspect that getting five lines plotted was fallout from the bug you had with `sin` vs `sind` and the way the conditions were defined. If the original `if` and `elseif` conditions weren’t hit for a particular `x` value, then the function would return `nothing`. In some cases you can use values like `nothing` to break a single line in Plots.jl into multiple.