sorting floats numerically - not in ascii order - in python

Question

This might sound like a silly question, but I've tried to find an answer that works without much success. I've got a list of lists:

for v in sorted(list):
    print v


[885.1, 12824]
[885.1, 19843]
[885.11, 1319]
[885.12, 1155]
[885.13, 12844]
[885.14, 33602]
[885.15, 11324]
[885.16, 44040]
[885.2, 119283]
[885.3, 8424]

I've iterated through my list using the sorted function - however that brings up the items in ASCII order as above - can they be sorted as floats in a human readable order? ie:

[885.1, 19843]
[885.2, 119283]
[885.3, 8424]
[885.11, 1319]
[885.12, 1155]
[885.13, 12844]
[885.14, 33602]
[885.15, 11324]
[885.16, 44040]

Do I need to create an index of somekind? Convert my floats to ints? Any help much appreciated.

David.

The original sort is already ordered numerically - 885.16 is less than 885.2(0) — Feanor
– Feanor, Commented Sep 7, 2011 at 6:06
In your input list you have two values in which 885.1 appears first. I assume you want those to both appear in your output, right? And you want them to be considered when sorting, correct? — Ray Toal
– Ray Toal, Commented Sep 7, 2011 at 6:25

HYRY · Accepted Answer · 2011-09-07 06:29:58Z

3

convert the float to string first and split it by ".":

sorted(a, key=lambda x:map(int, str(float(x[0])).split(".")))

edited Sep 7, 2011 at 6:29

answered Sep 7, 2011 at 6:15

HYRY

97.9k28 gold badges197 silver badges192 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Gabi Purcaru · Accepted Answer · 2011-09-07 06:03:15Z

1

This is called a "natsort" (natural sort). A quick google on it gives me this: http://www.skynet.ie/~caolan/Packages/python-natsort.html (haven't tried it though). Maybe it helps you.

^{Oh and that's not necessarily ASCII sort, it's just the number order, you know, like the real axis}

answered Sep 7, 2011 at 6:03

Gabi Purcaru

31.7k9 gold badges81 silver badges96 bronze badges

Comments

Swiss · Accepted Answer · 2011-09-07 06:08:48Z

1

You need to give sorted a comparison function. Something like the following:

sorted(list, cmp=lambda x, y: cmp(x[0], y[0]))

Just write the function you need for what you want and plug it in.

You'll probably want something like a reverse radix sort.

answered Sep 7, 2011 at 6:08

Swiss

5,9091 gold badge32 silver badges46 bronze badges

Comments

Ray Toal · Accepted Answer · 2011-09-07 06:22:55Z

1

This is kind of a hack, but:

a = [
    [885.1, 19843],
    [885.1, 12824],
    [885.11, 1319],
    [885.12, 1155],
    [885.13, 12844],
    [885.14, 33602],
    [885.15, 11324],
    [885.16, 44040],
    [885.2, 119283],
    [882.8, 8424],
    [882.75, 8424],
    [885.3, 8424]
]

for v in sorted(a, key=lambda t: str(t[0]).split(".")[0] + ("%05d" % int(str(t[0]).split(".")[1])) + "," + str(t[1])):
    print v

Result is

[882.8, 8424]
[882.75, 8424]
[885.1, 12824]
[885.1, 19843]
[885.2, 119283]
[885.3, 8424]
[885.11, 1319]
[885.12, 1155]
[885.13, 12844]
[885.14, 33602]
[885.15, 11324]
[885.16, 44040]

Disclaimer: this assumes at most 5 places after the decimal point. Adjust accordingly.

answered Sep 7, 2011 at 6:22

Ray Toal

88.7k20 gold badges186 silver badges245 bronze badges

Collectives™ on Stack Overflow

sorting floats numerically - not in ascii order - in python

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related