How do I use colorbar attributes such as in this snippet:
import seaborn as sns
uniform_data = np.random.rand(10, 12) # random data
ax = sns.heatmap(uniform_data)
cbar = ax.collections[0].colorbar
plt.show()
To shrink the colorbar and put it to the bottom and anchored to the lower left corner (that is, NOT centered)?
Something like this, but with the colorbar shrunk to, let's say 70% and anchored to the bottom left
I am unsure how to search for the methods as cbar.set_location() is not available.
If you want infinite customizability, you need to go more low level than you will get with seaborn, which gives convenience, but can't have knobs for everything.
The most straightforward way to get what you want is to place the colorbar axes manually. Note that you will need to play with the y offset, which I set here to -0.2.
import matplotlib.pyplot as plt
import numpy as np
uniform_data = np.random.rand(10, 12) # random data
fig, ax = plt.subplots(layout='constrained')
pc = ax.imshow(uniform_data)
cbax = ax.inset_axes([0, -0.2, 0.7, 0.05], transform=ax.transAxes)
fig.colorbar(pc, ax=ax, cax=cbax, shrink=0.7, orientation='horizontal')
plt.show()
You could create the colorbar via seaborn, extract its position, adapt it and set it again:
from matplotlib import pyplot as plt
import seaborn as sns
import numpy as np
uniform_data = np.random.rand(10, 12)
ax = sns.heatmap(uniform_data, cmap='rocket_r', cbar_kws={'orientation': 'horizontal', 'ticks': np.linspace(0, 1, 6)})
cax = ax.collections[0].colorbar.ax # get the ax of the colorbar
pos = cax.get_position() # get the original position
cax.set_position([pos.x0, pos.y0, pos.width * 0.6, pos.height]) # set a new position
cax.set_frame_on(True)
cax.invert_xaxis() # invert the direction of the colorbar
for spine in cax.spines.values(): # show the colorbar frame again
spine.set(visible=True, lw=.8, edgecolor='black')
plt.show()
Note that you need cbar_kws={'orientation': 'horizontal'} for a horizontal colorbar that by default is aligned with the x-axis.
After using .set_position, something like plt.tight_layout() won't work anymore.
About your new questions:
cax.invert_xaxis() doesn't invert the colorbar direction
Yes it does. You seem to want to reverse the colormap. Matplotlib's convention is to append _r to the colormap name. In this case, seaborn is using the rocket colormap, rocket_r would be the reverse. Note that changing the ticks doesn't work the way you try it, as these are just numeric positions which will be sorted before they are applied.
If you want to show 0 and 1 in the colorbar (while the values in the heatmap are e.g. between 0.001 and 0.999, you could use vmin and vmax. E.g. sns.heatmap(..., vmin=0, vmax=1). vmin and vmax are one way to change the mapping between the values and the colors. By default, vmin=data.min() and vmax=data.max().
To show the colorbar outline: Add a black frame around a colorbar
ax.collections[0].colorbar is a colorbar, which in the latest versions also supports some functions to set ticks
ax.collections[0].colorbar.ax is an Axes object (a subplot). Matplotlib creates a small subplot on which the colorbar will be drawn. axs support a huge number of functions to change how the subplot looks or to add new elements. Note that a stackoverflow answer isn't meant to put of full matplotlib tutorial. The standard tutorials could be a starting point.
Related
I want to make a plot with a grid of thumbnails on the left and a line plot on the right. Here is a minimal example
import numpy as np
from matplotlib import pyplot as plt
### This can change at runtime
n_grid = 4
### Grid of thumbnails
fig = plt.figure(figsize=(20,10.2))
for i in range(n_grid):
for j in range(n_grid):
ax = plt.subplot2grid(shape=(n_grid, 2*n_grid), loc=(i,j))
plt.imshow(np.random.random((16,16)))
ax.set_axis_off()
### Line plot
ax = plt.subplot2grid(shape=(n_grid, 2*n_grid), loc=(0,n_grid), rowspan=n_grid-1, colspan=n_grid)
plt.plot(np.cumsum(np.random.random(100)), label='Random Sum')
plt.xlim([0, 100])
plt.ylim(0,50)
plt.xlabel('Number', fontsize=12)
plt.ylabel('Sum', fontsize=12)
plt.figtext(0.5, 0.01, f'Unique identifier', ha='center', va='baseline')
#plt.tight_layout()
plt.subplots_adjust(left=0.01, bottom=0.03, right=0.99, top=0.99, wspace = 0.06, hspace=0.06)
plt.savefig('plot_1.png', dpi=96)
The problem is that the yticklabels and ylabel stick over the center into the area of the thumbnails. The lineplot on the right is too wide.
One common solution found on the internet is using automatic resizing with tight_layout(), so I change the last three lines to
plt.tight_layout()
#plt.subplots_adjust(left=0.01, bottom=0.03, right=0.99, top=0.99, wspace = 0.06, hspace=0.06)
plt.savefig('plot_2.png', dpi=96)
This does not rescale the lineplot, but instead makes the wspace and hspace attributes so big I get way too much whitespace between the thumbnails.
I am looking for a solution to either
Set wspace and hspace of only the right subplot, not all of them together, or
resize the lineplot to fit into the designated area, without the labels sticking out
It would seem that this is an easy problem, but despite searching for about 2 hours and digging around in the object properties with iPython I found nothing suitable. All solutions seem to change the size and padding of the subplots, not fitting a plot into the area defined with subplot2grid. The only other solution I can think of is a hack that calculates a modified aspect from the value ranges to make the lineplot always a given percentage thinner.
You can play around with subfigures. For example, if you do:
import numpy as np
from matplotlib import pyplot as plt
### This can change at runtime
n_grid = 4
### Grid of thumbnails
fig = plt.figure(figsize=(20,10.2))
# add 2 subfigures
subfigs = fig.subfigures(1, 2, wspace=0)
# add thumbnail grid into left subfig
gsLeft = subfigs[0].add_gridspec(n_grid, n_grid)
axLeft = []
for i in range(n_grid):
for j in range(n_grid):
axLeft.append(subfigs[0].add_subplot(gsLeft[i, j]))
axLeft[-1].imshow(np.random.random((16,16)))
axLeft[-1].set_axis_off()
### Line plot
gsRight = subfigs[1].add_gridspec(3, 1)
axRight = subfigs[1].add_subplot(gsRight[:2, 0])
axRight.plot(np.cumsum(np.random.random(100)), label='Random Sum')
axRight.set_xlim([0, 100])
axRight.set_ylim(0,50)
axRight.set_xlabel('Number', fontsize=12)
axRight.set_ylabel('Sum', fontsize=12)
# adjust subfigures here (play around with these to get the desired effect)
subfigs[0].subplots_adjust(wspace=0.03, hspace=0.03, bottom=0.05, top=0.95, left=0.05, right=0.95)
subfigs[1].subplots_adjust(left=0.01)
# add title (here I've had to add it to the left figure, so it's not centred,
# in my test adding it to the figure itself meant it was not visible, although
# the example in the Matplotlib docs suggests it should work!)
# fig.suptitle(f'Unique identifier', x=0.5, y=0.025, ha='center', va='baseline')
subfigs[0].suptitle(f'Unique identifier', x=0.5, y=0.025, ha='center', va='baseline')
fig.savefig("plot_1.png", dpi=150)
This gives:
but you can play around with the values to adjust it as you like.
I am quite new to python programming. I have a script with me that plots out a heat map using matplotlib. Range of X-axis value = (-180 to +180) and Y-axis value =(0 to 180). The 2D heatmap colours areas in Rainbow according to the number of points occuring in a specified area in the x-y graph (defined by the 'bin' (see below)).
In this case, x = values_Rot and y = values_Tilt (see below for code).
As of now, this script colours the 2D-heatmap in the linear scale. How do I change this script such that it colours the heatmap in the log scale? Please note that I only want to change the heatmap colouring scheme to log-scale, i.e. only the number of points in a specified area. The x and y-axis stay the same in linear scale (not in logscale).
A portion of the code is here.
rot_number = get_header_number(headers, AngleRot)
tilt_number = get_header_number(headers, AngleTilt)
psi_number = get_header_number(headers, AnglePsi)
values_Rot = []
values_Tilt = []
values_Psi = []
for line in data:
try:
values_Rot.append(float(line.split()[rot_number]))
values_Tilt.append(float(line.split()[tilt_number]))
values_Psi.append(float(line.split()[psi_number]))
except:
print ('This line didnt work, it may just be a blank space. The line is:' + line)
# Change the values here if you want to plot something else, such as psi.
# You can also change how the data is binned here.
plt.hist2d(values_Rot, values_Tilt, bins=25,)
plt.colorbar()
plt.show()
plt.savefig('name_of_output.png')
You can use a LogNorm for the colors, using plt.hist2d(...., norm=LogNorm()). Here is a comparison.
To have the ticks in base 2, the developers suggest adding the base to the LogLocator and the LogFormatter. As in this case the LogFormatter seems to write the numbers with one decimal (.0), a StrMethodFormatter can be used to show the number without decimals. Depending on the range of numbers, sometimes the minor ticks (shorter marker lines) also get a string, which can be suppressed assigning a NullFormatter for the minor colorbar ticks.
Note that base 2 and base 10 define exactly the same color transformation. The position and the labels of the ticks are different. The example below creates two colorbars to demonstrate the different look.
import matplotlib.pyplot as plt
from matplotlib.ticker import NullFormatter, StrMethodFormatter, LogLocator
from matplotlib.colors import LogNorm
import numpy as np
from copy import copy
# create some toy data for a standalone example
values_Rot = np.random.randn(100, 10).cumsum(axis=1).ravel()
values_Tilt = np.random.randn(100, 10).cumsum(axis=1).ravel()
fig, (ax1, ax2) = plt.subplots(ncols=2, figsize=(15, 4))
cmap = copy(plt.get_cmap('hot'))
cmap.set_bad(cmap(0))
_, _, _, img1 = ax1.hist2d(values_Rot, values_Tilt, bins=40, cmap='hot')
ax1.set_title('Linear norm for the colors')
fig.colorbar(img1, ax=ax1)
_, _, _, img2 = ax2.hist2d(values_Rot, values_Tilt, bins=40, cmap=cmap, norm=LogNorm())
ax2.set_title('Logarithmic norm for the colors')
fig.colorbar(img2, ax=ax2) # default log 10 colorbar
cbar2 = fig.colorbar(img2, ax=ax2) # log 2 colorbar
cbar2.ax.yaxis.set_major_locator(LogLocator(base=2))
cbar2.ax.yaxis.set_major_formatter(StrMethodFormatter('{x:.0f}'))
cbar2.ax.yaxis.set_minor_formatter(NullFormatter())
plt.show()
Note that log(0) is minus infinity. Therefore, the zero values in the left plot (darkest color) are left empty (white background) on the plot with the logarithmic color values. If you just want to use the lowest color for these zeros, you need to set a 'bad' color. In order not the change a standard colormap, the latest matplotlib versions wants you to first make a copy of the colormap.
PS: When calling plt.savefig() it is important to call it before plt.show() because plt.show() clears the plot.
Also, try to avoid the 'jet' colormap, as it has a bright yellow region which is not at the extreme. It may look nice, but can be very misleading. This blog article contains a thorough explanation. The matplotlib documentation contains an overview of available colormaps.
Note that to compare two plots, plt.subplots() needs to be used, and instead of plt.hist2d, ax.hist2d is needed (see this post). Also, with two colorbars, the elements on which the colorbars are based need to be given as parameter. A minimal change to your code would look like:
from matplotlib.ticker import NullFormatter, StrMethodFormatter, LogLocator
from matplotlib.colors import LogNorm
from matplotlib import pyplot as plt
from copy import copy
# ...
# reading the data as before
cmap = copy(plt.get_cmap('magma'))
cmap.set_bad(cmap(0))
plt.hist2d(values_Rot, values_Tilt, bins=25, cmap=cmap, norm=LogNorm())
cbar = plt.colorbar()
cbar.ax.yaxis.set_major_locator(LogLocator(base=2))
cbar.ax.yaxis.set_major_formatter(StrMethodFormatter('{x:.0f}'))
cbar.ax.yaxis.set_minor_formatter(NullFormatter())
plt.savefig('name_of_output.png') # needs to be called prior to plt.show()
plt.show()
I'm trying to place a legend just above the ax in matplotlib using ax.legend(loc=(0, 1.1)); however, if I change the figure size from (5,5) to (5,10) the legend shows up at a different distance from the top edge of the plot.
Is there any way to reference the top edge of the plot and offset it a set distance from it?
Thanks
There is a constant distance between the legend bounding box and the axes by default. This is set via the borderaxespad parameter. This defaults to the rc value of rcParams["legend.borderaxespad"], which is usually set to 0.5 (in units of the fontsize).
So essentially you get the behaviour you're asking for for free. Mind however that you should specify the loc to the corner of the legend from which that padding is to be taken. I.e.
import numpy as np
import matplotlib.pyplot as plt
for figsize in [(5,4), (5,9)]:
fig, ax = plt.subplots(figsize=figsize)
ax.plot([1,2,3], label="label")
ax.legend(loc="lower left", bbox_to_anchor=(0,1))
plt.show()
For more detailed explanations on how to position legend outside the axes, see How to put the legend out of the plot. Also relevant: How to specify legend position in matplotlib in graph coordinates
I would like to minimize white space in my figure. I have a row of sub plots where four plots share their y-axis and the last plot has a separate axis.
There are no ylabels or ticklabels for the shared axis middle panels.
tight_layout creates a lot of white space between the the middle plots as if leaving space for tick labels and ylabels but I would rather stretch the sub plots. Is this possible?
import matplotlib.gridspec as gridspec
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns
fig = plt.figure()
gs = gridspec.GridSpec(1, 5, width_ratios=[4,1,4,1,2])
ax = fig.add_subplot(gs[0])
axes = [ax] + [fig.add_subplot(gs[i], sharey=ax) for i in range(1, 4)]
axes[0].plot(np.random.randint(0,100,100))
barlist=axes[1].bar([1,2],[1,20])
axes[2].plot(np.random.randint(0,100,100))
barlist=axes[3].bar([1,2],[1,20])
axes[0].set_ylabel('data')
axes.append(fig.add_subplot(gs[4]))
axes[4].plot(np.random.randint(0,5,100))
axes[4].set_ylabel('other data')
for ax in axes[1:4]:
plt.setp(ax.get_yticklabels(), visible=False)
sns.despine();
plt.tight_layout(pad=0, w_pad=0, h_pad=0);
Setting w_pad = 0 is not changing the default settings of tight_layout. You need to set something like w_pad = -2. Which produces the following figure:
You could go further, to say -3 but then you would start to get some overlap with your last plot.
Another way could be to remove plt.tight_layout() and set the boundaries yourself using
plt.subplots_adjust(left=0.065, right=0.97, top=0.96, bottom=0.065, wspace=0.14)
Though this can be a bit of a trial and error process.
Edit
A nice looking graph can be achieved by moving the ticks and the labels of the last plot to the right hand side. This answer shows you can do this by using:
ax.yaxis.tick_right()
ax.yaxis.set_label_position("right")
So for your example:
axes[4].yaxis.tick_right()
axes[4].yaxis.set_label_position("right")
In addition, you need to remove sns.despine(). Finally, there is now no need to set w_pad = -2, just use plt.tight_layout(pad=0, w_pad=0, h_pad=0)
Using this creates the following figure:
From the matplotlib command summary for the colorbar method I am aware that the keyword argument orientation := 'horizontal' | 'vertical' as a parameter places an horizontal bar underneath the plot or a vertical to the right of it respectively.
Yet, in my situation, I would rather place the colour bar at the opposite side of the default (without too much fiddling... if possible).
How could I code this? Am I missing some obvious feature?
I've found another method that avoids having to manually edit axes locations, and instead allows you to keep the colorbar linked to an existing plot axis by using the location keyword (method adapted initially from here).
The location argument is meant to be used on colorbars which reference multiple axes in a list (and will throw an error if colorbar is given only one axis), but if you simply put your one axis in a list, it will allow you to use the argument. You can use the following code as an example:
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = fig.add_subplot(111)
axp = ax.imshow(np.random.randint(0, 100, (100, 100)))
cb = plt.colorbar(axp,ax=[ax],location='left')
plt.show()
which yields this plot:
:
I think the easiest way is to make sure the colorbar is in its own axis. You can adapt from this example:
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
ax = fig.add_subplot(111)
axp = ax.imshow(np.random.randint(0, 100, (100, 100)))
# Adding the colorbar
cbaxes = fig.add_axes([0.1, 0.1, 0.03, 0.8]) # This is the position for the colorbar
cb = plt.colorbar(axp, cax = cbaxes)
plt.show()
which results in this: