Filling an array with arrays in numpy?

Question

A rather simple problem, and yet I dont seem to find any solution to it:

I am trying to use the differentiation of two arrays within an array and insert it as a new result into a new array... I hope the code clarifies this intention, even though it is not working, as python is telling me that it cannot combine a sequence with array calculation... How can I go around this problem? Thanks in advance!

MeteorNum = 5
#Coordinate Setup:

XPos = np.random.randint(0, 600, (MeteorNum,1))
YPos = np.random.randint(0, 800, (MeteorNum,1))

XYPos = np.hstack((XPos,YPos))
XYPos = np.vstack((XYPos, XYPos[0]))
print XYPos

#Distances:
r = np.zeros((MeteorNum,MeteorNum))

for i in range(0, MeteorNum):
    for x in range(0, MeteorNum):
        r[x,i] = (XYPos[x,:] - XYPos[i,:])
r = r*10**5
print r

and here the error I get:

runfile('C:/Users/Marco DS/Dropbox/1_TUDelft/4Q/AE1205 Python/python codes      2015/bonus assigments/week_5 Gravity simu.py', wdir='C:/Users/Marco   DS/Dropbox/1_TUDelft/4Q/AE1205 Python/python codes 2015/bonus assigments')
[[249 660]
 [256 605]
 [119 423]
 [422 398]
 [480 504]
 [249 660]]
Traceback (most recent call last):

  File "<ipython-input-57-4cd9cc29ece0>", line 1, in <module>
    runfile('C:/Users/Marco DS/Dropbox/1_TUDelft/4Q/AE1205 Python/python     codes 2015/bonus assigments/week_5 Gravity simu.py', wdir='C:/Users/Marco     DS/Dropbox/1_TUDelft/4Q/AE1205 Python/python codes 2015/bonus assigments')

  File "C:\Users\Marco DS\Anaconda\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 682, in runfile
execfile(filename, namespace)

File "C:\Users\Marco DS\Anaconda\lib\site-    packages\spyderlib\widgets\externalshell\sitecustomize.py", line 71, in execfile
exec(compile(scripttext, filename, 'exec'), glob, loc)

  File "C:/Users/Marco DS/Dropbox/1_TUDelft/4Q/AE1205 Python/python codes 2015/bonus assigments/week_5 Gravity simu.py", line 37, in <module>
r[x,i] = (XYPos[x,:] - XYPos[i,:])

ValueError: setting an array element with a sequence.

Answer 1

try to add dtype= in the container array:

MeteorNum = 5
#Coordinate Setup:

XPos = nprand.randint(0, 600, (MeteorNum,1))
YPos = nprand.randint(0, 800, (MeteorNum,1))

XYPos = np.hstack((XPos,YPos))
XYPos = np.vstack((XYPos, XYPos[0]))
print XYPos

#Distances:
r = np.zeros((MeteorNum,MeteorNum),dtype=np.ndarray)

for i in range(0, MeteorNum):
    for x in range(0, MeteorNum):
        r[x,i] = (XYPos[x,:] - XYPos[i,:])
r = r*10**5
print r

EDIT

The dtype argument indicate the desired data-type for the array, eg, numpy.int8. Default is numpy.float64.

Answer 2

To remove errors, I think you need an extra dimension, of size 2, in your array r :

r = np.zeros((MeteorNum,MeteorNum,2))

As XYPos[x,:] - XYPos[i,:] in your for loop has a shape of (2,)

This returns a single array of shape (5, 5, 2) .