Re: [Numpy-discussion] appending extra items to arrays
So it seems like lists are the way to grow an array. Interestingly enough, it is very easy to grown an array in Matlab. Any idea how they do that (or are they slow as well?). Mark On Oct 11, 8:53 pm, Adam Mercer [EMAIL PROTECTED] wrote: On 11/10/2007, Mark Janikas [EMAIL PROTECTED] wrote: If you do not know the size of your array before you finalize it, then you should use lists whenever you can. I just cooked up a short example: snip # Result # Total Time with array: 2.12951189331 Total Time with list: 0.0469707035741 Hope this helps, That is helpful, I thought that using arrays would be much faster but its clearly not in this case. Thanks Adam ___ Numpy-discussion mailing list [EMAIL PROTECTED]://projects.scipy.org/mailman/listinfo/numpy-discussion ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
Growing an array by appending it is the slow way in matlab. The suggested way to do things there is preallocate the array by saying x=zeros() and then referencing the elements in the array and inserting the correct value. --Chad Kidder On Oct 17, 2007, at 7:16 AM, mark wrote: So it seems like lists are the way to grow an array. Interestingly enough, it is very easy to grown an array in Matlab. Any idea how they do that (or are they slow as well?). Mark On Oct 11, 8:53 pm, Adam Mercer [EMAIL PROTECTED] wrote: On 11/10/2007, Mark Janikas [EMAIL PROTECTED] wrote: If you do not know the size of your array before you finalize it, then you should use lists whenever you can. I just cooked up a short example: snip # Result # Total Time with array: 2.12951189331 Total Time with list: 0.0469707035741 Hope this helps, That is helpful, I thought that using arrays would be much faster but its clearly not in this case. Thanks Adam ___ ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
Hello, I work with numarray.zeros(n, numarray.Float64) as sound mixers ; there are huge number of datas : 44 000 .. 192 000 /second Operations : add, append, add append (if the mixing begins on the existing part of the array + append if the array has to be prolonged) I do never use list-appending but I concatenate a zero-array with a fixed length (which can be given e.g. sr/10 ) This way is much more faster then appending with lists if there are huge number of datas (for small arrays, lists are faster, but I have never a sound of 10 samples :-) -- René Bastian http://www.musiques-rb.org http://pythoneon.musiques-rb.org ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
On 10/10/07, Anne Archibald [EMAIL PROTECTED] wrote:
On 11/10/2007, Robert Kern [EMAIL PROTECTED] wrote:
Appending to a list then converting the list to an array is the most
straightforward way to do it. If the performance of this isn't a
problem, I
recommend leaving it alone.
Just a speculation:
Python strings have a similar problem - they're immutable, and so are
even more resistant to growth than numpy arrays. For those situations
where you really really want to grow a srting, python provides
StringIO, where you keep efficiently adding to the string, then
finalize it to get the real string out. Would something analogous be
interesting for arrays?
Have you looked at array.array?
import array
a = array.array('i')
a.append(2)
a.append(7)
a
array('i', [2, 7])
--
. __
. |-\
.
. [EMAIL PROTECTED]
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Re: [Numpy-discussion] appending extra items to arrays
On 11/10/2007, Robert Kern [EMAIL PROTECTED] wrote: Appending to a list then converting the list to an array is the most straightforward way to do it. If the performance of this isn't a problem, I recommend leaving it alone. Thanks, I'll leave it as is - I was just wondering if there was a better way to do it. Cheers Adam ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
If you do not know the size of your array before you finalize it, then
you should use lists whenever you can. I just cooked up a short
example:
##
import timeit
import numpy as N
values = range(1)
def appendArray(values):
result = N.array([], dtype=int)
for value in values:
result = N.append(result, value)
return result
def appendList(values):
result = []
for value in values:
result.append(value)
return N.array(result)
test = timeit.Timer('appendArray(values)',
'from __main__ import appendArray, values')
t1 = test.timeit(number=10)
test2 = timeit.Timer('appendList(values)',
'from __main__ import appendList, values')
t2 = test2.timeit(number=10)
print Total Time with array: + str(t1)
print Total Time with list: + str(t2)
# Result #
Total Time with array: 2.12951189331
Total Time with list: 0.0469707035741
Hope this helps,
MJ
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Adam Mercer
Sent: Thursday, October 11, 2007 7:42 AM
To: Discussion of Numerical Python
Subject: Re: [Numpy-discussion] appending extra items to arrays
On 11/10/2007, Robert Kern [EMAIL PROTECTED] wrote:
Appending to a list then converting the list to an array is the most
straightforward way to do it. If the performance of this isn't a
problem, I
recommend leaving it alone.
Thanks, I'll leave it as is - I was just wondering if there was a
better way to do it.
Cheers
Adam
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Re: [Numpy-discussion] appending extra items to arrays
On 11/10/2007, Mark Janikas [EMAIL PROTECTED] wrote: If you do not know the size of your array before you finalize it, then you should use lists whenever you can. I just cooked up a short example: snip # Result # Total Time with array: 2.12951189331 Total Time with list: 0.0469707035741 Hope this helps, That is helpful, I thought that using arrays would be much faster but its clearly not in this case. Thanks Adam ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
[Numpy-discussion] appending extra items to arrays
Hi In some code I have, I need to append some extra data to a given array. At the moment I construct the data in a list, append the extra information I need and then convert the final list to an array. Is there a way that I can append extra information to an existing array thereby negating the need for the list, as the array object doesn't seem to have an append() method? Cheers Adam ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
Adam Mercer wrote: Hi In some code I have, I need to append some extra data to a given array. At the moment I construct the data in a list, append the extra information I need and then convert the final list to an array. Is there a way that I can append extra information to an existing array thereby negating the need for the list, as the array object doesn't seem to have an append() method? Fundamentally, numpy works because its underlying data is in a block of memory. This is incompatible with appending data at will, which is the exact thing lists are good at. Now, depending on the problem you are trying to solve, it may be better (read faster, more memory efficient, etc...) to use numpy arrays, and create new bigger ones when you need to append data. It all depends on your problem. cheers, David ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
Adam Mercer wrote: Hi In some code I have, I need to append some extra data to a given array. At the moment I construct the data in a list, append the extra information I need and then convert the final list to an array. Is there a way that I can append extra information to an existing array thereby negating the need for the list, as the array object doesn't seem to have an append() method? Appending to a list then converting the list to an array is the most straightforward way to do it. If the performance of this isn't a problem, I recommend leaving it alone. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
On 11/10/2007, Robert Kern [EMAIL PROTECTED] wrote: Appending to a list then converting the list to an array is the most straightforward way to do it. If the performance of this isn't a problem, I recommend leaving it alone. Just a speculation: Python strings have a similar problem - they're immutable, and so are even more resistant to growth than numpy arrays. For those situations where you really really want to grow a srting, python provides StringIO, where you keep efficiently adding to the string, then finalize it to get the real string out. Would something analogous be interesting for arrays? Anne P.S. A (somewhat) slow python implementation would be fairly easy to write. -A ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] appending extra items to arrays
Anne Archibald wrote: On 11/10/2007, Robert Kern [EMAIL PROTECTED] wrote: Appending to a list then converting the list to an array is the most straightforward way to do it. If the performance of this isn't a problem, I recommend leaving it alone. Just a speculation: Python strings have a similar problem - they're immutable, and so are even more resistant to growth than numpy arrays. For those situations where you really really want to grow a srting, python provides StringIO, where you keep efficiently adding to the string, then finalize it to get the real string out. Would something analogous be interesting for arrays? The Python version of StringIO, at least, just keeps a list, too. The primary benefit of StringIO is that it exposes the file interface. For building up a string/array, using the list is just as convenient (and for arrays, probably more convenient given the variety of shapes one might want to build) and at least as readable. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
