Float-step range function

By fallopiano on Feb 28th, 2010 12:12 am

Here I have a simple range function that can use floats as steps or increments. In a time test (using Psyco 1.6, python 2.5, and a basic PC), the normal frange function was able to go up to 1,000,000 from 0, by .3 , and finish that in about 0.5929 seconds. I did the same with the more minimalistic version and got a slightly lower average time; about 0.5310 seconds. So about .1165 times faster than the normal version. Note also that the frange function can go from high to low; ie frange(10,-3,.25). It can also do the basic frange(-3,10,.25) and frange(10,.5)

# both frange functions written by Luke Endres (fallopiano)
# If your going to use it, please give credit!
def frange(start, end=None, step=None):
    'A range function that can accept float increments'
    if end == None:
        end = start
        start = 0.0

    if step == None:
        step = 1.0
    L = []
    n = float(start)

    if end > start:
        while n < end:
            L.append(n)
            n += step
        return L
    elif end < start:
        while n > end:
            L.append(n)
            n -= step
        return L

# ------------------------------------------------------------- #
# a slightly faster, more minimalistic version of frange...


def frange_mini(start,end=None,step=None):
    'A range function that can accept float increments'
    if end==None:
        end=start
        start=0.0
    if step==None:step=1.0
    L=[]
    n=float(start)
    if end>start:
        while n<end:
            L.append(n)
            n+=step
        return L
    elif end<start:
        while n>end:
            L.append(n)
            n-=step
        return L

2 Years Ago

actually disregard that last little bit of text, 'frange(10,.5) '. I meant to say 'frange(10,step = -.5)', because without 'step = -.5', it would turn up an infinite loop. At line 5, please add:

if start and not end:
    print 'frange error: got start argument but not end'
    exit()

Also, if you are trying to go up from zero to a number by a float, please declare what is the start/end/step argument. IE use 'frange(0,10,.5)' not 'frange(10,.5)'

fallopiano

Junior Poster in Training

68 posts since Jun 2009

Reputation Points: 10

Solved Threads: 6

2 Years Ago

even more minimalistic while still keeping the fastest speed would be:

def frange(s,e=None,S=None):
    if e==None:e=s;s=0.0
    if S==None:S=1.0
    L=[];n=s
    if e>s:
        while n<e:L.append(n);n+=S
    elif e<s:
        while n>e:L.append(n);n-=S
    return L

fallopiano

Junior Poster in Training

68 posts since Jun 2009

Reputation Points: 10

Solved Threads: 6

2 Years Ago

There is a nasty bug in all your approaches to frange() ...

# both frange functions written by Luke Endres (fallopiano)
# If your going to use it, please give credit!
def frange(start, end=None, step=None):
    'A range function that can accept float increments'
    if end == None:
        end = start
        start = 0.0

    if step == None:
        step = 1.0
    L = []
    n = float(start)

    if end > start:
        while n < end:
            L.append(n)
            n += step
        return L
    elif end < start:
        while n > end:
            L.append(n)
            n -= step
        return L

# testing ...
# would expect numbers 6.0 to 6.3, but 6.4 slips through!
for k in frange(6.0, 6.4, 0.1):
    print(k)

"""my result -->
6.0
6.1
6.2
6.3
6.4  oops!!!
"""

vegaseat

DaniWeb's Hypocrite

Moderator

5,989 posts since Oct 2004

Reputation Points: 1,345

Solved Threads: 1,417

2 Years Ago

I have another frange function. I remember writing it after reading a discussion about frange functions in the activestate code snippets

def frange (start ,stop ,n ):
    """frange(start, stop, n) -> list of n float
    A range function which returns n equally spaced floating numbers
    from start to stop"""
    L =[0.0 ]*n 
    nm1 =n -1 
    nm1inv =1.0 /nm1 
    start ,stop =start *nm1inv ,stop *nm1inv 
    for i in range (n ):
      L [i ]=(start *(nm1 -i )+stop *i )
    return L

It was included in the P1function class in this other snippet http://www.daniweb.com/code/snippet217163.html . The idea of passing the number of points instead of a step is to avoid the problem mentioned above.
Note that range could be replaced by xrange if python < 3.

Gribouillis

Posting Maven

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