Re: Accumulate function in python
In article 7xpqyjgvjm@ruckus.brouhaha.com, Paul Rubin no.em...@nospam.invalid wrote: I think Peter Otten's solution involving a generator is the one most in the current Python spirit. It's cleaner (for my tastes) than the ones that use things like list.append. Agreed -- Aahz (a...@pythoncraft.com) * http://www.pythoncraft.com/ Normal is what cuts off your sixth finger and your tail... --Siobhan -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On Wed, Jul 21, 2010 at 8:17 AM, John Nagle na...@animats.com wrote: On 7/19/2010 9:56 AM, dhruvbird wrote: On Jul 19, 9:12 pm, Brian Victorhomeusen...@brianhv.org wrote: dhruvbird wrote: Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. Yes, even I have noticed that reduce is a tad under-used function. Yes, I had a use case for it once, but it wasn't worth the trouble. map is often useful, but reduce, not so much. Python isn't really a functional language. There's no bias toward functional solutions, lambdas aren't very general, and the performance isn't any better. Nor is any concurrency provided by map or reduce. So there's no win in trying to develop cute one-liners. Too bad about the lack of concurrency, would be many places where that would be nice. Geremy Condra -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
geremy condra, 27.07.2010 12:54: On Wed, Jul 21, 2010 at 8:17 AM, John Nagle wrote: On 7/19/2010 9:56 AM, dhruvbird wrote: On Jul 19, 9:12 pm, Brian Victor wrote: dhruvbird wrote: Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. Yes, even I have noticed that reduce is a tad under-used function. Yes, I had a use case for it once, but it wasn't worth the trouble. map is often useful, but reduce, not so much. Python isn't really a functional language. There's no bias toward functional solutions, lambdas aren't very general, and the performance isn't any better. Nor is any concurrency provided by map or reduce. So there's no win in trying to develop cute one-liners. Too bad about the lack of concurrency, would be many places where that would be nice. Besides the many places where the current properties match just fine, there are some places where concurrency would be helpful. So I wouldn't call it lack of concurrency, as that seems to imply that it's a missing feature in what both builtins are targeted to provide. Just use one of the map-reduce frameworks that are out there if you need concurrency in one way or another. Special needs are not what builtins are there for. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On 19 Jul, 13:18, dhruvbird dhruvb...@gmail.com wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. At least for large arrays, this is the kind of task where NumPy will help. import numpy as np np.cumsum([ 0, 1, 2, 1, 1, 0, 0, 2, 3 ]) array([ 0, 1, 3, 4, 5, 5, 5, 7, 10]) -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On Jul 21, 8:17 pm, John Nagle na...@animats.com wrote: On 7/19/2010 9:56 AM, dhruvbird wrote: On Jul 19, 9:12 pm, Brian Victorhomeusen...@brianhv.org wrote: dhruvbird wrote: Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. Yes, even I have noticed that reduce is a tad under-used function. Yes, I had a use case for it once, but it wasn't worth the trouble. map is often useful, but reduce, not so much. Python isn't really a functional language. There's no bias toward functional solutions, lambdas aren't very general, and the performance isn't any better. Nor is any concurrency provided by map or reduce. So there's no win in trying to develop cute one-liners. Yes agreed. However, there is: 1. now scope for optimization (for example returning generators instead of lists) at every stage if using functions -- these functions can be internally changed as long as the external guarantees they provide remain essentially unchanged. 2. readability wins because you express your intent (operations) rather than anything else. For example, if I want the product of the square roots of all odd integers in an array, I can say: answer = reduce(product, map(math.sqrt, filter(lambda x: x%2 == 0, some_array_with_ints))) While I agree that python may not have been initially seen as a functional language, it is powerful and flexible enough to be one or at least decently support such paradigms. Regards, -Dhruv. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On 7/19/2010 9:56 AM, dhruvbird wrote: On Jul 19, 9:12 pm, Brian Victorhomeusen...@brianhv.org wrote: dhruvbird wrote: Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. Yes, even I have noticed that reduce is a tad under-used function. Yes, I had a use case for it once, but it wasn't worth the trouble. map is often useful, but reduce, not so much. Python isn't really a functional language. There's no bias toward functional solutions, lambdas aren't very general, and the performance isn't any better. Nor is any concurrency provided by map or reduce. So there's no win in trying to develop cute one-liners. John Nagle -- http://mail.python.org/mailman/listinfo/python-list
Accumulate function in python
Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Regards, -Dhruv. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
Hi, you may want to do like this array=[0,1,2] sumArray = [] for element in range(0,len(array)): if element == 0 : sumArray.append(array[element]) else: sumArray.append((array[element] + sumArray[element-1])) and then you can recheck it Thanks, nitin On Mon, Jul 19, 2010 at 4:48 PM, dhruvbird dhruvb...@gmail.com wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Regards, -Dhruv. -- http://mail.python.org/mailman/listinfo/python-list -- Nitin Pawar -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
dhruvbird wrote: I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Homework? def cumulative_sum(values, start=0): ... for v in values: ... start += v ... yield start ... list(cumulative_sum([ 0, 1, 2, 1, 1, 0, 0, 2, 3 ])) [0, 1, 3, 4, 5, 5, 5, 7, 10] Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
2010/7/19 dhruvbird dhruvb...@gmail.com: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Regards, -Dhruv. -- Hi, just a straightworward, naive approach...: lst_int = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] acc_int = 0 output_lst = [] for i in lst_int: acc_int += i output_lst.append(acc_int) print output_lst vbr -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
Am 19.07.2010 13:18, dhruvbird wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. python import copy import itertools def acc(items, copy=copy.deepcopy): items = iter(items) result = next(items) yield copy(result) for item in items: result += item yield copy(result) print list(acc([0, 1, 2, 1, 1, 0, 0, 2, 3])) print list(itertools.islice(acc(itertools.count()), 10)) print list(acc(['a', 'b', 'c'])) print list(acc([[a], [b], [c]])) /python Output: [0, 1, 3, 4, 5, 5, 5, 7, 10] [0, 1, 3, 6, 10, 15, 21, 28, 36, 45] ['a', 'ab', 'abc'] [[a], [a, b], [a, b, c]] Without copy.deepcopy() the last line would be: [[a, b, c], [a, b, c], [a, b, c]] The copy=copy.deepcopy parameter allows for things like this: print list(acc([[a], [b], [c]], tuple)) [(a,), (a, b), (a, b, c)] or: print list(acc([['a'], ['b'], ['f'], ['s'], ['c'], ['g']], max)) ['a', 'b', 'f', 's', 's', 's'] or: data = [[0], [1], [2], [1], [1], [2], [3]] print list(acc(data, lambda x: float(sum(x)) / float(len(x [0.0, 0.5, 1.0, 1.0, 1.0, 1.1667, 1.4285714285714286] Endless possibilities in an endless universe. Regards, Mick. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On 07/19/2010 01:18 PM, dhruvbird wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Regards, -Dhruv. Maybe not pythonic, but straight-forward: import numpy numpy.cumsum(x) array([ 0, 1, 3, 4, 5, 5, 5, 7, 10]) An example with a class class CumulativeSum(object): def __init__(self, start=0): self._current = start def __call__(self, value): self._current += value return self._current cummulative_sum = CumulativeSum(0) map(cummulative_sum, x) [0, 1, 3, 4, 5, 5, 5, 7, 10] Dirty: current = 0 def cummulative_sum(value): global current current += value return current map(cummulative_sum, x) [0, 1, 3, 4, 5, 5, 5, 7, 10] Weird: def cummulative_sum_reducer(x, y): x.append(x[-1] + y) return x reduce(cummulative_sum_reducer, x, [0]) [0, 0, 1, 3, 4, 5, 5, 5, 7, 10] Cheers Andre -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On Mon, 19 Jul 2010 04:18:48 -0700, dhruvbird wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] [pedant] The above are *lists*, not arrays. Python has arrays, but you have to call import array to get them. [/pedant] What is the best way (or pythonic way) to get this. Others have given you a plethora of advanced, complicated and obscure ways to solve this question, but I haven't seen anyone give the simplest method (simple as in no tricks or advanced features): data = [0, 1, 2, 1, 1, 0, 0, 2, 3] csums = [] for x in data: if csums: y = x + csums[-1] else: y = x csums.append(y) We can save some code with the ternary operator: data = [0, 1, 2, 1, 1, 0, 0, 2, 3] csums = [] for x in data: csums.append((x + csums[-1]) if csums else x) Here's a version that writes the cumulative sum in place: data = [0, 1, 2, 1, 1, 0, 0, 2, 3] for i in range(1, len(data)): data[i] += data[i-1] -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
dhruvbird wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Now that Steven's given you the simple, pythonic way, I'll just mention the advanced, complicated and obscure way that might be vaguely familiar if you're coming from a functional programming background: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] def running_sum(result, current_value): return result + [result[-1]+current_value if result else current_value] reduce(running_sum, x, []) Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. -- Brian -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On Jul 19, 9:12 pm, Brian Victor homeusen...@brianhv.org wrote: dhruvbird wrote: Hello, I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Now that Steven's given you the simple, pythonic way, I'll just mention the advanced, complicated and obscure way that might be vaguely familiar if you're coming from a functional programming background: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] def running_sum(result, current_value): return result + [result[-1]+current_value if result else current_value] reduce(running_sum, x, []) Having offered this, I don't recall ever seeing reduce used in real python code, and explicit iteration is almost always preferred. Yes, even I have noticed that reduce is a tad under-used function. So, I guess no function like accumulate below exists in the standard lib. def accumulate(proc, seed, seq): ret = [] for i in seq: ret.append(proc(seed, i)) return ret x = [0, 1, 3, 4, 5, 5, 5, 7, 10] print accumulate(lambda x,y: x+y, 0, x) My guess is that accumulate can be used in many more scenarios. Regards, -Dhruv. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
On Jul 19, 4:28 pm, Peter Otten __pete...@web.de wrote: dhruvbird wrote: I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Homework? not really :) It's just that I was wondering if a built-in function for doing such things (which I find myself doing increasingly with an explicit loop) exists. Regards, -Dhruv. def cumulative_sum(values, start=0): ... for v in values: ... start += v ... yield start ... list(cumulative_sum([ 0, 1, 2, 1, 1, 0, 0, 2, 3 ])) [0, 1, 3, 4, 5, 5, 5, 7, 10] Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
dhruvbird dhruvb...@gmail.com wrote: On Jul 19, 4:28 pm, Peter Otten __pete...@web.de wrote: dhruvbird wrote: I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Homework? not really :) It's just that I was wondering if a built-in function for doing such things (which I find myself doing increasingly with an explicit loop) exists. Why would you find yourself doing it more than once? Write it once in a function and then just re-use the code. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
Brian Victor homeusen...@brianhv.org writes: def running_sum(result, current_value): return result + [result[-1]+current_value if result else current_value] reduce(running_sum, x, []) That is not really any good because Python lists are actually vectors, so result+[...] actually copies the whole old list, making your function take quadratic time. It would be ok in a FP language where lists were chains of cons nodes and result+[...] just allocated a single cons. I think Peter Otten's solution involving a generator is the one most in the current Python spirit. It's cleaner (for my tastes) than the ones that use things like list.append. -- http://mail.python.org/mailman/listinfo/python-list
Re: Accumulate function in python
Peter Otten wrote: dhruvbird wrote: I have a list of integers: x = [ 0, 1, 2, 1, 1, 0, 0, 2, 3 ] And would like to compute the cumulative sum of all the integers from index zero into another array. So for the array above, I should get: [ 0, 1, 3, 4, 5, 5, 5, 7, 10 ] What is the best way (or pythonic way) to get this. Homework? def cumulative_sum(values, start=0): ... for v in values: ... start += v ... yield start ... list(cumulative_sum([ 0, 1, 2, 1, 1, 0, 0, 2, 3 ])) [0, 1, 3, 4, 5, 5, 5, 7, 10] Peter nice! Peter -- http://mail.python.org/mailman/listinfo/python-list
