Why doesn't this simple scatter plot work in a sane way? It seems like I'm having to jump through hoops for something that ought to "just work". I think the code below should result in plot with (0,0) as the origin and an x and y axis that each go up to 10 with nicely labeled, evenly spaced tick marks on each axis. Instead, the origin is at 1,7 and the x axis is backwards, decreasing from right to left.
Maybe I'm going blind, but I've looked through the Tutorials and Gallery and I can't find any example of a plain, simple, no-frills plot of distinct points on a coordinate plane.
x = ['7', '8', '6', '7.5', '4']
y = ['1', '2', '2', '3', '3']
plt.scatter(x,y)
plt.xlim(0,10)
plt.ylim(0,10)
plt.show()
I have also tried
plt.plot(x,y, 'ro')
plt.axis([0,10,0,10])
plt.show()
with similar results.
I've been able to get sane looking results by calling plt.gca().invert_xaxis() to get the x axis into an increasing rather than decreasing direction and manually passing a list of tickmarks to xticks and yticks, but I don't understand why that's necessary. Why doesn't setting the max and min for the x and y axis result in a graph with sensible default tick marks?
Your lists are of strings, not numbers so matplotlib doesn't really know how to handle them in the way that you expect. Remove the single quotes from the x and y lists and try it again.
Related
Say you have the matrix given by three arrays, being:
x = N-dimensional array.
y = M-dimensional array.
And z is a set of "somewhat random" values from -0.3 to 0.3 in a NxM shape. I need to create a plot in which the x values are in the x-axis, y values are in the y-axis and using z as the source to indicate the intensity of each pixel with a color map.
So far, I have tried using
plt.contourf(x,y,z)
and the resulting plot is very nice for me (attached at the end of this paragraph), but a smoothing is automatically applied to the plot! I need to be able to distinguish the pixels and I cannot find a way to do it.
contourf result
I have also studied the possibility of using
ax.matshow(z)
in order to sucesfully see the pixels... but then I am struggling trying to personalize the x and y axis, since only the index of the pixel is shown (see below).
matshow result
Would you please give me some ideas? Thank you.
Without more information on your x,y data it's hard to know, but I would guess you are looking for pcolormesh.
plt.pcolormesh(x,y,z)
This would take the x and y data as input and hence shows the z data at the appropriate coordinates.
You can use imshow with the keyword interpolation='nearest'.
plt.imshow(z, interpolation='nearest')
I am trying to plot some data but I only have my x and y axis given. I would like to get the frequency for my z axis like I would in a histogram. But I don't really want a histogram, rather a scatter plot or a surface plot.
This is my histogram right now, quite messy.
Is it possible to use the function of the histogram to get the frequency of the points but have a scatter/surface plot instead? Or to change the bars of the histogram to something like dots or something similar?
None of my data points have the same value, so I would like them to be sorted in intervals, like [0,0.05] or so, that's why I am trying to find another solution than calculating this.
I'm making plots where the (0,0) position is not necessarily in the bottom left corner of the plot frame, meaning that the x and y axes and their ticks cross within the plot frame. It's fine to have the lines, ticks and their values within the frame, but having the axis titles so near to their lines interferes with visualization of certain data points.
I'd simply like to force the x and y axis titles to be at the bottom and far left of the plot frame, respectively; it doesn't work to simply 'pad' the xlabel or ylabel titles because the padding I'd need would vary between plots.
How to get the titles always in these consistent locations of the plot frame, even if the corresponding axis lines, ticks/values may vary in the plot frame space?
Thank you.
I'd like to add a note here. It seemed to me that it could be possible to define the xlabel and ylabel 'labelpad' values directly from the data range:
For example, one could find the minimum x-value of the minimum y-value (this would set the position of the x-axis label), and the minimum x-value of the minimum x-value (this would set the position of the y-axis label):
xpad = ax.get_ylim()[0]
ypad = ax.get_xlim()[0]
Then use these values in xlabel and ylabel parameters as labelpads:
pylab.xlabel("X Title", fontsize=12, labelpad=abs(xpad))
pylab.ylabel("Y Title", fontsize=12, labelpad=abs(ypad))
Unfortunately, it doesn't look like labelpad can accept variables. Any suggestions that might allow a work-around?
i am using MPAndroid charting toolkit for data visualization. chart plotting smooth in MPAndroid but problem arise when i try plot dual y axis(left& right). As right axis appear data points on spread over the x axis completely. all data points appearing on the left of chart. How can i spread the data points ?
mChart = (LineChart) findViewById(R.id.Chart);
mChart.setGridBackgroundColor(Color.parseColor("#F4F4F4"));
mChart.setDrawGridBackground(false);
mChart.setTouchEnabled(true);
mChart.setHighlightEnabled(false);
mChart.setDragEnabled(false);
mChart.setScaleEnabled(true);
mChart.setPinchZoom(true);
mChart.setDescription("");
mChart.getAxisLeft().setAxisMaxValue(YMaxValue);
mChart.getAxisLeft().setAxisMinValue(YMinValue);
mChart.getAxisLeft().setStartAtZero(false);
mChart.getAxisRight().setEnabled(false);
if(General.InnerClass.Y2AxisValues.size()>0)
{
mChart.getAxisRight().setEnabled(true);
mChart.getAxisRight().setSpaceBottom(12.25f);
mChart.getAxisRight().setAxisMaxValue(Y2MaxValue);
mChart.getAxisRight().setAxisMinValue(Y2MinValue);
mChart.getAxisRight().setStartAtZero(false);
mChart.getXAxis().setAvoidFirstLastClipping(true);
}
mChart.setData(data);
progbar.setVisibility(View.GONE);
mChart.invalidate();
Before
After
The data points are exactly where they should be. The only thing that has changed is the range of values that is displayed on each axis.
--> this range is now significationly lower because only one set of data is represented by each axis, before, one axis had to scale large enough to display both datasets.
I suggest you read the documentation of the YAxis and simply increase the range of values that should be displayed on the axis.
while plotting y2 axis providing the x values is the problem. values for the x axis should be provide for single time. providing twice add the values to x axis exiting values get doubled.
thnx #philipp
Is there a way to render the tick labels just right inside the axes, i.e, something like the direction property there is on the ticks themself?
Right now I'm setting the x property to a positive value on the ticklabels to draw them inside of the axis, i.e.,
ax2.set_yticklabels(['0', '2500', '5000', '7500'], minor=False, x=0.05)
But this doesn't really work on resizable plots, as the 0.05 figure is absolute (and too big on big plots).
Any ideas?
I'm assuming that ax2 is constructed as ax2 = ax.twinx(), which is to say that it is on the right side of the axes.
You could do something like the following:
ax2.set_yticklabels(['0', '2500', '5000', '7500'], minor=False, horizontalalignment='right')
for tick in ax2.yaxis.get_major_ticks():
tick.set_pad(-8)
If you want the left side axis on the inside too, then you'd simply switch the horizontal alignment to 'left' and change the pad from -8 to -25.
The two numbers might not be exact and could depend on other matplotlib settings you might have (e.g. length of major ticks) so you may want to increase or decrease those values slightly.