matplotlib: format axis offset-values to whole numbers or specific number
PythonMatplotlibPython Problem Overview
I have a matplotlib figure which I am plotting data that is always referred to as nanoseconds (1e-9). On the y-axis, if I have data that is tens of nanoseconds, ie. 44e-9, the value on the axis shows as 4.4 with a +1e-8 as an offset. Is there anyway to force the axis to show 44 with a +1e-9 offset?
The same goes for my x-axis where the axis is showing +5.54478e4, where I would rather it show an offset of +55447 (whole number, no decimal - the value here is in days).
I've tried a couple things like this:
p = axes.plot(x,y)
p.ticklabel_format(style='plain')
for the x-axis, but this doesn't work, though I'm probably using it incorrectly or misinterpreting something from the docs, can someone point me in the correct direction?
Thanks, Jonathan
I tried doing something with formatters but haven't found any solution yet...:
myyfmt = ScalarFormatter(useOffset=True)
myyfmt._set_offset(1e9)
axes.get_yaxis().set_major_formatter(myyfmt)
and
myxfmt = ScalarFormatter(useOffset=True)
myxfmt.set_portlimits((-9,5))
axes.get_xaxis().set_major_formatter(myxfmt)
On a side note, I'm actually confused as to where the 'offset number' object actually resides...is it part of the major/minor ticks?
Python Solutions
Solution 1 - Python
I had exactly the same problem, and these lines fixed the problem:
from matplotlib.ticker import ScalarFormatter
y_formatter = ScalarFormatter(useOffset=False)
ax.yaxis.set_major_formatter(y_formatter)
Solution 2 - Python
A much easier solution is to simply customize the tick labels. Take this example:
from pylab import *
# Generate some random data...
x = linspace(55478, 55486, 100)
y = random(100) - 0.5
y = cumsum(y)
y -= y.min()
y *= 1e-8
# plot
plot(x,y)
# xticks
locs,labels = xticks()
xticks(locs, map(lambda x: "%g" % x, locs))
# ytikcs
locs,labels = yticks()
yticks(locs, map(lambda x: "%.1f" % x, locs*1e9))
ylabel('microseconds (1E-9)')
show()
Notice how in the y-axis case, I multiplied the values by 1e9
then mentioned that constant in the y-label
EDIT
Another option is to fake the exponent multiplier by manually adding its text to the top of the plot:
locs,labels = yticks()
yticks(locs, map(lambda x: "%.1f" % x, locs*1e9))
text(0.0, 1.01, '1e-9', fontsize=10, transform = gca().transAxes)
EDIT2
Also you can format the x-axis offset value in the same manner:
locs,labels = xticks()
xticks(locs, map(lambda x: "%g" % x, locs-min(locs)))
text(0.92, -0.07, "+%g" % min(locs), fontsize=10, transform = gca().transAxes)
Solution 3 - Python
You have to subclass ScalarFormatter
to do what you need... _set_offset
just adds a constant, you want to set ScalarFormatter.orderOfMagnitude
. Unfortunately, manually setting orderOfMagnitude
won't do anything, as it's reset when the ScalarFormatter
instance is called to format the axis tick labels. It shouldn't be this complicated, but I can't find an easier way to do exactly what you want... Here's an example:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import ScalarFormatter, FormatStrFormatter
class FixedOrderFormatter(ScalarFormatter):
"""Formats axis ticks using scientific notation with a constant order of
magnitude"""
def __init__(self, order_of_mag=0, useOffset=True, useMathText=False):
self._order_of_mag = order_of_mag
ScalarFormatter.__init__(self, useOffset=useOffset,
useMathText=useMathText)
def _set_orderOfMagnitude(self, range):
"""Over-riding this to avoid having orderOfMagnitude reset elsewhere"""
self.orderOfMagnitude = self._order_of_mag
# Generate some random data...
x = np.linspace(55478, 55486, 100)
y = np.random.random(100) - 0.5
y = np.cumsum(y)
y -= y.min()
y *= 1e-8
# Plot the data...
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x, y, 'b-')
# Force the y-axis ticks to use 1e-9 as a base exponent
ax.yaxis.set_major_formatter(FixedOrderFormatter(-9))
# Make the x-axis ticks formatted to 0 decimal places
ax.xaxis.set_major_formatter(FormatStrFormatter('%0.0f'))
plt.show()
Which yields something like:
Whereas, the default formatting would look like:
Hope that helps a bit!
Edit: For what it's worth, I don't know where the offset label resides either... It would be slightly easier to just manually set it, but I couldn't figure out how to do so... I get the feeling that there has to be an easier way than all of this. It works, though!
Solution 4 - Python
Similar to Amro's answer, you can use FuncFormatter
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import FuncFormatter
# Generate some random data...
x = np.linspace(55478, 55486, 100)
y = np.random.random(100) - 0.5
y = np.cumsum(y)
y -= y.min()
y *= 1e-8
# Plot the data...
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x, y, 'b-')
# Force the y-axis ticks to use 1e-9 as a base exponent
ax.yaxis.set_major_formatter(FuncFormatter(lambda x, pos: ('%.1f')%(x*1e9)))
ax.set_ylabel('microseconds (1E-9)')
# Make the x-axis ticks formatted to 0 decimal places
ax.xaxis.set_major_formatter(FuncFormatter(lambda x, pos: '%.0f'%x))
plt.show()
Solution 5 - Python
Gonzalo's solution started working for me after having added set_scientific(False)
:
ax=gca()
fmt=matplotlib.ticker.ScalarFormatter(useOffset=False)
fmt.set_scientific(False)
ax.xaxis.set_major_formatter(fmt)
Solution 6 - Python
As has been pointed out in the comments and in this answer, the offset may be switched off globally, by doing the following:
matplotlib.rcParams['axes.formatter.useoffset'] = False
Solution 7 - Python
I think that a more elegant way is to use the ticker formatter. Here is an example for both xaxis and yaxis:
from pylab import *
from matplotlib.ticker import MultipleLocator, FormatStrFormatter
majorLocator = MultipleLocator(20)
xFormatter = FormatStrFormatter('%d')
yFormatter = FormatStrFormatter('%.2f')
minorLocator = MultipleLocator(5)
t = arange(0.0, 100.0, 0.1)
s = sin(0.1*pi*t)*exp(-t*0.01)
ax = subplot(111)
plot(t,s)
ax.xaxis.set_major_locator(majorLocator)
ax.xaxis.set_major_formatter(xFormatter)
ax.yaxis.set_major_formatter(yFormatter)
#for the minor ticks, use no labels; default NullFormatter
ax.xaxis.set_minor_locator(minorLocator)
Solution 8 - Python
For the second part, without manually resetting all the ticks again, this was my solution:
class CustomScalarFormatter(ScalarFormatter):
def format_data(self, value):
if self._useLocale:
s = locale.format_string('%1.2g', (value,))
else:
s = '%1.2g' % value
s = self._formatSciNotation(s)
return self.fix_minus(s)
xmajorformatter = CustomScalarFormatter() # default useOffset=True
axes.get_xaxis().set_major_formatter(xmajorformatter)
obviously you can set the format string to whatever you want.