[Numpy-discussion] arrays are column-wise or row-wise?
Brian Blais
bblais at bryant.edu
Tue Mar 28 06:03:14 CST 2006
Hello,
I thought I had read somewhere that the values in a numpy contiguous array are stored
column-wise (moving down from the upper left to the lower left first) like C as
opposed to row-wise (moving right from the upper left to the upper right first).
However, when I write a simply Pyrex function to access the data pointer and print it
out, it seems to go across the row. Is this correct? I am using numpy 0.9.3 and
Python 2.3 on Linux. This also occurs for Numeric. I post the code below, with the
sample output.
thanks,
bb
--
-----------------
bblais at bryant.edu
http://web.bryant.edu/~bblais
#test_numpy.pyx:
cdef extern from "numpy/arrayobject.h":
struct PyArray_Descr:
int type_num, elsize
char type
ctypedef class numpy.ArrayType [object PyArrayObject]:
cdef char *data
cdef int nd
cdef int *dimensions, *strides
cdef object base
cdef PyArray_Descr *descr
cdef int flags
def test_numpy(ArrayType x):
cdef int i
cdef double *data
cdef int length
data=<double *>x.data
length=x.dimensions[0]*x.dimensions[1]
for i from 0 <= i < length:
print data[i]
#------------------------------------------------------
#testit.py:
import numpy
from test_numpy import *
a=numpy.array([[1,2,3],[4,5,6],[7,8,9],[10,11,12]],numpy.Float64)
print a
test_numpy(a)
#------------------------------------------------------
#output from program:
>>> execfile('testit.py')
[[ 1. 2. 3.]
[ 4. 5. 6.]
[ 7. 8. 9.]
[ 10. 11. 12.]]
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
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