plotting numpy.ndarray

Question

I do n-operations on matrices which results in the output of n of 2x1 matrices. I append them to a list and want to plot as points with x,y coordinate. I found I need to convert them to a numpy.array so I finish with nx2 ndarray and want to plot [:0] and [:1]. When I print results everything seems to be correct when I try to plot I finish with blank figure and no points at all. I noticed that ndarrays are separated by space not by comma but not sure how to interpret it. My code looks like:

import numpy as np
import pylab as pl

class GetMat(object):
    def __init__(self):
        self.Posp = np.matrix([[1,1],[1,1]])
        self.Velp = np.matrix([[1],[1]])
    def __call__(self):
        self.Posp = self.Posp*np.random.random()
        self.Velp = self.Velp*np.random.random()
        return self.Posp,self.Velp
    def __repr__(self):
        return "Posp = \n%s \nVelp = \n%s" % (self.Posp,self.Velp)
class Data(object):
    def __init__(self):
        self.x = 0
    def __call__(self,P,V):
        self.x = P*V
        return self.x[0,0], self.x[1,0]
    def __repr__(self):
        return "x = %s" % self.x

def Test():
    Nsamples = np.arange(0,10,1)
    newMat = GetMat()
    dataToPlot = Data()
    Xsaved = []
    for i in range(len(Nsamples)):
        z1,z2 = newMat()
        position, velocity = dataToPlot(z1,z2)
        Xsaved.append([position, velocity])
    print 'Xsaved = %s' % Xsaved
    print 'tyep Xsaved %s' % type(Xsaved)
    XsavedArr = np.array(Xsaved)
    print 'XsavedArr %s' % XsavedArr
    print 'tyep XsavedArr %s' % type(XsavedArr)
    print 'XsavedArr[:,0] = %s' % XsavedArr[:,0]
    print 'XsavedArr[:,1] = %s' % XsavedArr[:,1]
    pl.plot(np.array(XsavedArr[:,0]),np.array(XsavedArr[:,1]), linestyle='x-',label = 'Xsaved')
    pl.show()

if __name__ == '__main__':
    Test()

I expect normal plot of random numbers not a blank. I can't find how to plot having ndarrays in form of nx2 matrix

unutbu · Accepted Answer · 2012-10-23 15:51:49Z

3

I'm not sure what kind of line style you are looking for, but you'll see something if you change the linestyle to:

linestyle='-'

Or, if you wish to see the data points marked with x, just remove the keyword linestyle:

pl.plot(np.array(XsavedArr[:,0]),np.array(XsavedArr[:,1]),
        'x-',label = 'Xsaved')

answered Oct 23, 2012 at 15:51

unutbu

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