In GNU Octave you can make a picture where different colors represent different values in a matrix. You can also add a colorbar, which shows what color corresponds to what value.
Is it possible to somehow add units to the values shown in the colorbar? Instead of saying “0.36” it would say “0.36 V/nm”? I know this is possible in Matlab, but I can’t figure out how to do it in Octave. Any good workarounds?
I assume someone here will mention that I should use matplotlib instead (that usually happens). How would you accomplish the same thing with that?
The matplotlib answer (using pylab) is
imshow(random((20,20)))
colorbar(format='%.2f V/nm')
In Octave it seems that the following works (but I'm no Octave expert so maybe there's a better way):
c=colorbar();
labels = {};
for v=get(c,'ytick'), labels{end+1} = sprintf('%.2f V/nm',v); end
set(c,'yticklabel',labels);
Related
I'm constructing a graph plot in Julia and need to color each edge of the graph differently, based on some weighting factor. I can't find a way to get a specific RGB (or HSV, it doesn't matter) value from a colormap. Let's say I'd like to get the RGB value on 'jet' that would correspond to a data value of n on imshow plot.
In python, I would just use jet(n), where n is the value along the colormap in which I am interested. PyPlot in Julia doesn't seem to have wrapped this functionality. I've also already tried indexing into the cmap object returned from get_cmap(). Any advice?
I'm stumped, so even an approximate solution would help. Thanks!
Maybe you can look at the Colors.jl package (https://github.com/JuliaGraphics/Colors.jl):
using Colors
palette = colormap("Oranges", 100)
Then you can access each color with palette[n]. Or are you using PyCall? A code describing what you're trying to do would help.
I have three 2d arrays: X,Y,Z, which contain irregular 3d points coordinate,respectively.And another 2d array data, which contains the values on those points.
What I want to do is to display this data in 3d space , with 0 value part masked out.Much like this one:
In matlab, I can use function fill3 to achieve this, but how can I plot the same kind of picture in matplotlib or mayavi ? I have tried to use mask array ,plot_surface and colorface together, as the example here:
Plotting a masked surface plot using python, numpy and matplotlib
and it worked, the result is the link below:
but that is really really slow, and will cost too much time. Is there a better way?
Well, today I find out an alternative way to solve the problem. Except using plot_surface, I choose to use scatter3D,
the core code is some what like this
aa=np.shape(X)[0]
bb=np.shape(X)[1]
x=X.reshape(aa*bb)
y=Y.reshape(aa*bb)
z=Z.reshape(aa*bb)
data=data.reshape(aa*bb)
x1=[]
y1=[]
z1=[]
da1=[]
for i in range(aa*bb):
if data[i]>0:
x1.append(x[i])
y1.append(y[i])
z1.append(z[i])
da1.append(data[i])
my_cmap=cm.jet
my_cmap.set_over('c')
my_cmap.set_under('m')
N=da1/max(da1)
fig=plt.figure()
ax=fig.add_subplot(111,projection='3d')
ax.scatter3D(x1,y1,z1,s=6,alpha=0.8,marker=',',facecolors=my_cmap(N),lw=0)
and the result is like this:
this doesn't really solve the problem, but it is a nice substitution.
I'll keep waiting for more answers.
This question already has an answer here:
Embed matplotlib figure in larger figure
(1 answer)
Closed 8 years ago.
How can I use a matplotlib Figure object as a subplot? Specifically, I have a function that creates a matplotlib Figure object, and I would like to include this as a subplot in another Figure.
In short, here's stripped-down pseudocode for what I've tried:
fig1 = plt.figure(1, facecolor='white')
figa = mySeparatePlottingFunc(...)
figb = mySeparatePlottingFunc(...)
figc = mySeparatePlottingFunc(...)
figd = mySeparatePlottingFunc(...)
fig1.add_subplot(411, figure=figa)
fig1.add_subplot(412, figure=figb)
fig1.add_subplot(413, figure=figc)
fig1.add_subplot(414, figure=figd)
fig1.show()
Sadly, however, this fails. I know for a fact the individual plots returned from the function invocations are viable--I did a figa.show(),...,figd.show() to confirm that they are OK. What I get for the final line in the above code block--fig1.show()--is
a collection of four empty plots that have frames and x- and y- tickmarks/labels.
I've done quite a bit of googling around, and experimented extensively, but it's clear that I've missed something that is either really subtle, or embarrassingly obvious (I'll be happy for it to be the latter as long as I can get un-stuck).
Thanks for any advice you can offer!
You can't put a figure in a figure.
You should modify your plotting functions to take axes objects as an argument.
I am also unclear why the kwarg figure is there, I think it is an artifact of the way that inheritance works, the way that the documentation is auto-generated, and the way some of the getter/setter work is automated. If you note, it says figure is undocumented in the Figure documentation, so it might not do what you want;). If you dig down a bit, what that kwarg really controls is the figure that the created axes is attached too, which is not what you want.
In general, moving existing axes/artists between figures is not easy, there are too many bits of internal plumbing that need to be re-connected. I think it can be done, but will involving touching the internals and there is no guarantee that it will work with future versions or that you will get warning if the internals change in a way that will break it.
You need to your plotting functions to take an Axes object as argument. You can use a pattern like:
def myPlotting(..., ax=None):
if ax is None:
# your existing figure generating code
ax = gca()
so if you pass in an Axes object it gets drawn to (the new functionality you need), but if you don't all of your old code will work as expected.
I want to generate a grid of plots, of several arrays, with positive and negative values, with log scale, sharing the same colorbar.
I've achieved the sharing part of the colorbar (using ImageGrid and common max and min values), and I know that I could get a logarithmic scale using LogNorm() on the imshow call in the case of only positive values. But given the presence of negative values, I would need a colorbar on symmetric logarithmic scale.
I have found what would be the solution on https://stackoverflow.com/a/7741317/1101750 , but running the sample code Yann provides gives me very different results, cleary wrong:
Reviewing the code, I'm not able to grasp what's going on.
In addition to that, I've discovered that on Matplotlib 1.2, scale.SymmetricalLogScale.SymmetricalLogTransform asks for a new argument not explained on the documentation (linscale, which looking at the code of other transforms I assume that leaving it as 1 is a safe value).
Is the easiest solution subclassing LogNorm?
I've used a pretty simple recipe in the past to do exactly this, without the need to do any subclassing. matplotlib.colors.SymLogNorm provides most of the functionality you need, except that I've found it necessary to generate the tick marks by hand. Note that this solution uses matplotlib 1.3.0, and I may be using features that weren't available with 1.2.
def imshow_symlog(my_matrix, vmin, vmax, logthresh=5):
img=imshow( my_matrix ,
vmin=float(vmin), vmax=float(vmax),
norm=matplotlib.colors.SymLogNorm(10**-logthresh) )
maxlog=int(np.ceil( np.log10(vmax) ))
minlog=int(np.ceil( np.log10(-vmin) ))
#generate logarithmic ticks
tick_locations=([-(10**x) for x in xrange(minlog,-logthresh-1,-1)]
+[0.0]
+[(10**x) for x in xrange(-logthresh,maxlog+1)] )
cb=colorbar(ticks=tick_locations)
return img,cb
Since 1.3 matplotlib has a SymLogNorm. http://matplotlib.org/api/colors_api.html#matplotlib.colors.SymLogNorm
In an answer to an earlier question of mine regarding fixing the colorspace for scatter images of 4D data, Tom10 suggested plotting values as symbols in order to double-check my data. An excellent idea. I've run some similar demos in the past, but I can't for the life of me find the demo I remember being quite simple.
So, what's the easiest way to plot numerical values as the symbol in a scatter plot instead of 'o' for example? Tom10 suggested plt.txt(x,y,value)- and that is the implementation used in a number of examples. I however wonder if there's an easy way to evaluate "value" from my array of numbers? Can one simply say: str(valuearray) ?
Do you need a loop to evaluate the values for plotting as suggested in the matplotlib demo section for 3D text scatter plots?
Their example produces:
(source: sourceforge.net)
However, they're doing something fairly complex in evaluating the locations as well as changing text direction based on data. So, is there a cute way to plot x,y,C data (where C is a value often taken as the color in the plot data- but instead I wish to make the symbol)?
Again, I think we have a fair answer to this- I just wonder if there's an easier way?
The easiest way I've seen to do this is:
for x, y, val in zip(x_array, y_array, val_array):
plt.text(x, y, val)
Also, btw, you suggested using str(valarray), and this, as you may have noticed doesn't work. To convert an array of numbers to a sequence of strings you could use
valarray.astype(str)
to get a numpy array, or,
[str(v) for v in valarray]
to get a Python list. But even with valarray as a proper sequence of strings, plt.text won't iterate over it's inputs.