# Contour plots with varying locations for x-axis?
**URL:** https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686
**Category:** Visualization
**Tags:** plotting
**Created:** [May 23, 2021, 4:43pm UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686 "2021-05-23T16:43:57Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [May 23, 2021, 4:43pm UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/1 "2021-05-23T16:43:57Z")
Hi, I have a set of 2-dimensional data, defined over an array of timesteps, but at each timestep the position x-values are different. I’m trying to get contour plots, but the plots come up blank, and each time I get the error message: `Arrays have incorrect length or dimension.` An example code model excerpt goes like:
```julia
using Plots
tNum = 4; xNum = 3;
# These numbers will be >1000 in the real calc
FunctionForPlot = Array{Float64,2}(undef, tNum, xNum)
xValsArr = Array{Float64,2}(undef, tNum, xNum)
tValsArr = Array{Float64}(undef, tNum)
for i in 1:tNum
tValsArr[i] = i
for j in 1:xNum
xValsArr[i,j] = i + j^2
FunctionForPlot[i,j] = i*sin(35*j)
end
end
contour([xValsArr[i,j] for i=1:tNum, j=1:xNum],
[tValsArr[i] for i=1:tNum, j=1:xNum],
[FunctionForPlot[i,j] for i=1:tNum, j=1:xNum], fill=true)
```
Any suggestions on how to make this work, or why I’m not getting the plot I expected, would be welcome. Thank you!
---
### Author:  [@empet](https://discourse.julialang.org/u/empet)
#### Post date: [May 24, 2021, 2:43pm UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/2 "2021-05-24T14:43:22Z")
To draw the contour plot you must interpolate from your initial data, x, y, z, that define a function f(x[i,j], y[i, j])=z[i,j], the value of f at a regular grid, defined by
xi= 2:0.5:13, yi=1:4. I tried Dierckx.jl, but the Spline2D cannot be called because the flattened x-array contains the repeating value 5. Maybe Interpolations.jl provides an adequate function for 2D interpolation.
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [May 25, 2021, 7:34am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/3 "2021-05-25T07:34:10Z")
Hi empet, thanks for the response!
Thinking about it, it does seem likely that Julia cannot do contour plots (or similar 2D plots) on an irregularly-spaced grid (as defined by irregularly-spaced data), but that the data must somehow be interpolated to a regularly-spaced grid for contour (or similar) plots.
If that’s incorrect, and anyone does know how to extend contour plots to idiosyncratically-spaced data, please let me know…!
---
### Author:  [@empet](https://discourse.julialang.org/u/empet)
#### Post date: [May 25, 2021, 8:00am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/4 "2021-05-25T08:00:08Z")
Since I was not able to use Dierckx.jl and have no experience with Interpolations.jl (I’m a Julia beginner) I tried with Python `scipy.interpolate` and your contour plot looks like this:
The steps for getting a regular grid of values Xi, Yi, zi for which the Plots.jl contour could work:
```julia
x, y, z are the array passed by you as arguments for contour
xi = 2:0.5:13
yi = 1:0.5:4
fxy = scipy.interpolate.interp2d(x, y, z) #you should find the Interpolations.jl
#function that works like this scipy.interpolation function
zi = fxy(xi, yi)
Xi = xi' .* ones(length(yi))
Yi = ones(length(xi))'.*yi
contour(Xi, Yi, zi)
```
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [May 25, 2021, 8:28am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/5 "2021-05-25T08:28:16Z")
> [@CosmoProf](#):
>
> Julia cannot do contour plots (or similar 2D plots) on an irregularly-spaced grid (as defined by irregularly-spaced data)
The commonly used algorithm ([marching squares](https://en.wikipedia.org/wiki/Marching_squares)) requires a regular grid. There are other algorithms for eg triangle meshes, but for the purposes of plotting it is common to just approximate the surface and then compute on a regular grid.
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [May 25, 2021, 7:16pm UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/6 "2021-05-25T19:16:02Z")
Hi Tamas, thanks for the clarification. I understand what I have to do a little better now.
Empet, thanks for the sample scipy code, I’m sure this will come in handy for interpolating the data, which I plan to do soon.
I think I know how to proceed, thanks again guys!
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [June 3, 2021, 2:38am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/7 "2021-06-03T02:38:30Z")
Hi again, I’m revisiting this attempt, trying to mimic what I want with a 2D scatterplot (with distinct x and y values for each point), where the value of the function for each point is indicated by its color, on a color scale. I’ve searched online and tried doing this with `PGFPlotsX` and `Gadfly`, but I can’t find enough info to get the syntax right. Does anyone know how to get a simple example like the following to work:
```julia
using Plots
xData = [100.0*rand(Float64) for i in 1:100]
yData = [50.0*rand(Float64) for j in 1:100]
zData = [(xData[i] + yData[j]) for i=1:100, j=1:100]
scatter(xData , yData , color = zData) # This does NOT work, simplest fix??
```
It would also be nice if I could get each (variously colored) point to be plotted as a filled square (instead of just a point), so it would kind of look like a heatmap or contour plot (with gaps I guess).
Thanks for any suggestions…!
---
### Author:  [@empet](https://discourse.julialang.org/u/empet)
#### Post date: [June 7, 2021, 11:00am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/8 "2021-06-07T11:00:27Z")
@CosmoProf
I succeeded to define a plot following your requirement, using PlotlyJS.jl:
```julia
using PlotlyJS
m=75
n=100
xData = [100.0*rand(Float64) for i in 1:n]
yData = [50.0*rand(Float64) for j in 1:m]
X, Y = [x for y in yData, x in xData], [y for y in yData, x in xData]
zData = X+Y
trace = PlotlyJS.scatter(x=vec(X), y=vec(Y), mode="markers",
marker=attr(symbol="square", color=vec(zData),
showscale=true, colorbar_thickness=23))
pl = PlotlyJS.plot(trace, Layout(width=500, height=500, title_text="Your title",
xaxis=attr(range=[minimum(X), maximum(X)], showgrid=false),
yaxis=attr(range=[minimum(Y), maximum(Y)], showgrid=false)))
```
The above “heatmap” was defined with the default size for the marker.
Setting the marker attribute size=2.5, and the plasma colormap:
```julia
plasma=[[0.0, "#0c0786"],
[0.1, "#40039c"],
[0.2, "#6a00a7"],
[0.3, "#8f0da3"],
[0.4, "#b02a8f"],
[0.5, "#cb4777"],
[0.6, "#e06461"],
[0.7, "#f2844b"],
[0.8, "#fca635"],
[0.9, "#fcce25"],
[1.0, "#eff821"]]
```
the plot is as follows:
Your intuition was good, and the heatmap with gaps is very interesting 🙂
---
### Author:  [@BeastyBlacksmith](https://discourse.julialang.org/u/BeastyBlacksmith)
#### Post date: [June 7, 2021, 3:02pm UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/9 "2021-06-07T15:02:07Z")
If I got you right, the following should work
```julia
using Plots
xData = [100.0*rand(Float64) for i in 1:100]
yData = [50.0*rand(Float64) for j in 1:100]
zData = [(xData[i] + yData[j]) for i=1:100, j=1:100]
scatter(xData , yData , marker_z = zData, markershape = :square)
```
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [June 8, 2021, 4:17am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/10 "2021-06-08T04:17:24Z")
Hello BeastyBlacksmith, I tried your suggestion, but it does not seem to produce a proper 2-dimensional plot. If you replace the `zData` function with something sinusoidally-varying instead, it varies in the x-direction but not in the y-direction (it should do both). See the following example, which does not produce the fully two-dimensionally varying result expected:
```julia
using Plots
xData = [100.0*rand(Float64) for i in 1:1000]
yData = [50.0*rand(Float64) for j in 1:1000]
zData = [(sin(xData[i]/5)*cos(yData[j]/3)) for i=1:1000, j=1:1000]
scatter(xData , yData , marker_z = zData, markershape = :square)
```
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [June 8, 2021, 5:57am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/11 "2021-06-08T05:57:07Z")
I also tried creating a hybrid solution by putting empet’s suggestions together with Beasty’s, and I’m getting the same problem (no variation in the y-direction):
```julia
using Plots
nPix = 50
xData = [(100.0*(i/50)) for i in 1:nPix, j in 1:nPix]
yData = [(50.0*(j/27)) for j in 1:nPix, j in 1:nPix]
zData = [(sin(xData[i]/5)*cos(yData[j]/3)) for i=1:nPix, j=1:nPix]
x2D = vec(xData)
y2D = vec(yData)
z2D = vec(zData)
scatter(x2D, y2D, marker_z = z2D, markershape = :square)
```
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [June 8, 2021, 6:09am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/13 "2021-06-08T06:09:40Z")
BTW, this is actually more of what I had in mind… but I still can’t get the proper sine/cosine variation in the y-direction, for some reason:
```julia
using Plots
nPix = 50
xData = [(100.0*(i/50))*(j^(1/4)) for i in 1:nPix, j in 1:nPix]
yData = [(50.0*(j/27))*(i^(1/4)) for i in 1:nPix, j in 1:nPix]
zData = [(sin(xData[i]/5)*cos(yData[j]/3)) for i=1:nPix, j=1:nPix]
x2D = vec(xData)
y2D = vec(yData)
z2D = vec(zData)
scatter(x2D, y2D, marker_z = z2D, markershape = :square)
```
---
### Author:  [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)
#### Post date: [June 8, 2021, 6:20am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/14 "2021-06-08T06:20:12Z")
Oops, found my mistake…
```julia
using Plots
nPix = 50
xData = [(100.0*(i/50)) for i in 1:nPix, j in 1:nPix]
yData = [(50.0*(j/27)) for i in 1:nPix, j in 1:nPix]
zData = [(sin(xData[i,j]/5)*cos(yData[i,j]/3)) for i=1:nPix, j=1:nPix]
x2D = vec(xData)
y2D = vec(yData)
z2D = vec(zData)
scatter(x2D, y2D, marker_z = z2D, markershape = :square)
```
---
### Author:  [@empet](https://discourse.julialang.org/u/empet)
#### Post date: [June 8, 2021, 7:45am UTC](https://discourse.julialang.org/t/contour-plots-with-varying-locations-for-x-axis/61686/15 "2021-06-08T07:45:18Z")
Even if it was generated by a mistake, the previous one looks great.