I get a histogram picture in matplotlib which looks great. Now I realize I need a log scale on the y-axis, so I just add to the code:
ax.set_yscale('log')
but then, the histogram bars dissapear and I only get some sparse points, do you know waht could be the reason?
Thanks
Use hist's log=True keyword argument instead. This is a FAQ in matplotlib-user list :)
Related
I'm having some issues in setting the ticks in my plots using matplotlib. What I need is to set the ticks inwards, so inside the figure (but the labels must stay outside), and at the same time I need to have ticks on all four boundaries. Do you know a simple way to do this?
Thanks in advance!
Just because it can be useful for other people, I post here the simple solution I found after looking for some time in the documentation, as suggested by cfort:
ax.xaxis.set_ticks_position('both')
ax.xaxis.set_tick_params(direction='in', which='both', labelsize=16)
ax.yaxis.set_ticks_position('both')
ax.yaxis.set_tick_params(direction='in', which='both', labelsize=16)
ax.minorticks_on()
these lines of code set the tick inwards on both sides (e.g. for the x axis they are placed at top and bottom of the figure), set the label size and add the minorticks, which will point in the inward direction as well.
Let us suppose that I am plotting a few plots with pyplot/matplotlib. Now, the first has to have tick marks and tick labels, and only the first. The last has to have a colorbar and some marks for scale. If I do a script specifying the figure size, the plot proper in the last and first plots is drawn with smaller sizes, as the figure has to make room for the extra markings. And I seem to be not able to control that, in an automatic way, like making the other plots at the same scale inside a larger figure or something like that.
Example code (it looks a little non-pythonic because I am using PyPlot inside Julia):
using PyPlot
SomeData=randn(64,64,3)
for t=1:3
figure(figsize=(3.0,3.0))
imagen=imshow(SomeData[:,:,t], origin="lower")
if t!=3
xticks([])
yticks([])
else
tick_params(labelsize=8, direction="out")
end
if t==1
cbx=colorbar(imagen, fraction=0.045, ticks=[])
cbx[:set_label]("Some proper English Label", fontsize=8)
end
savefig("CSD-$t.svg",dpi=92)
end
Thanks in advance-
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'm trying to get and set the position of a draggable legend in matplotlib. My application consists of an interactive GUI, which has a redraw/plot function that should perform the follow steps:
save the position of the current legend.
clear the current axes and perform various plotting operations, which may or may add labels to their plots.
build a new draggable legend (ax.legend().draggable()) and restore the old position of the legend.
In between these steps the user is free to drag the legend around, and the goal is to persist the legend position when the plots are redrawn.
My first approach was to use oldpos = legend.get_bbox_to_anchor() and legend.set_bbox_to_anchor(oldpos) in steps 1 and 3. However this causes to move the legend completely off the visible area.
Note that I have to use ax.legend() and cannot use fig.legend(lines, labels), since step 2 is completely decoupled, i.e., I don't know anything about lines and labels in step 3. According to answers to the question How to position and align a matplotlib figure legend? there seems to be a difference between these two possibilities regarding axes or figure coordinates. Obviously my problem calls for figure coordinates, but I haven't fully understood how to convert the bbox to a "bbox in figure coordinates".
The even more severe problem I just realized is that apparently legend.get_bbox_to_anchor() always seems to return the same values irrespective of the drag position. So maybe the anchor can only be (ab-)used to manipulate the position of static legends? Is there another/proper way to save and restore the position of a draggable legend?
By looking at the implementation of Legend I found out that there is an undocumented property _loc, which exactly does what I want. My solution now looks astonishingly simple:
oldLegPos = ax.get_legend()._loc
# perform all plotting operations...
legend = ax.legend().draggable()
legend._loc = oldLegPos
It looks like _loc automatically stores figure coordinates, since I do not have to convert the coordinates in any way (eg. when the plotting operations completely change the axes ranges/coordinates).
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);