[Numpy-discussion] load from text files Pull Request Review
Christopher Barker
Chris.Barker@noaa....
Wed Sep 14 17:30:11 CDT 2011
On 9/14/11 2:41 PM, Benjamin Root wrote:
> Are you sure the f2 code works? a.resize() takes only a shape tuple. As
> coded, you should get an exception.
wow, what an idiot!
I think I just timed how long it takes to raise that exception...
And when I fix that, I get a memory error.
When I fix that, I find that f3() wasn't doing the right thing. What an
astonishing lack of attention on my part!
Here it is again, working, I hope!
In [107]: %timeit f1()
10 loops, best of 3: 50.7 ms per loop
In [108]: %timeit f2()
1000 loops, best of 3: 719 us per loop
In [109]: %timeit f3()
100 loops, best of 3: 19 ms per loop
So:
numpy.resize() is the slowest
numpy.empty+ numpy.append() is faster
numpy.ndarray.resize() is the fastest
Which matches my expectations, for once!
-Chris
The code:
#!/usr/bin/env python
"""
test_resize
A test of various numpy re-sizing options
"""
import numpy
def f1():
"""
numpy.resize
"""
extra = 100
l = extra
a = numpy.zeros((l,))
for i in xrange(100):
l += extra
a = numpy.resize(a, (l,) )
return a
def f2():
"""
numpy.ndarray.resize
"""
extra = 100
l = extra
a = numpy.zeros((l,))
for i in xrange(100):
l += extra
a.resize( (l,) )
return a
def f3():
"""
numpy.empty + append
"""
extra = 100
l = extra
a = numpy.zeros((l,))
for i in xrange(100):
b = numpy.empty((extra,))
a = numpy.append(a, b)
return a
a1 = f1()
a2 = f2()
a3 = f3()
if a1.shape == a2.shape == a3.shape:
print "they are all returning the same size array"
else:
print "Something is wrong!"
--
Christopher Barker, Ph.D.
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Chris.Barker@noaa.gov
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