Trying to sort a list by values closest to zero, using absolute value in python

Question

I've spent quite some time searching to see if there was a similar issue. Unfortunately, I couldn't just comment on the previously asked question to see why my attempt was not working. On this site there exists a question where a person wants to sort a list, according to closest numbers to a specific value. his example:not verbatim copying his example but putting a working solution

list_x = [1,2,5,11]
list_x.sort(key = lambda x: abs(x-4))

which will return the list sorted by values closest to 4 (5,2,1,11) However, when trying to sort a much larger list by values closest to zero this is happening to me:

listA.sort(key = lambda x: abs(x))

Traceback (most recent call last):
  File "<pyshell#382>", line 1, in <module>
    listA.sort(key = lambda x: abs(x))
  File "<pyshell#382>", line 1, in <lambda>
    listA.sort(key = lambda x: abs(x))
TypeError: bad operand type for abs(): 'str'

What exactly am I doing incorrectly thats preventing the list from being sorted by absolute values?

This is input data for what makes listA

for i in decrange(0, 13, i):
   code = (func(seq, float(i)))
   codes = '%.3f' % code
   listA.append(float(codes))
   listB.append(str(codes))
listA.sort(key = lambda k: abs(k))
x = listA[0]
answer = listB.index(x) * float(.01)

The input data would be helpful here. You may also call abs(int(x)). — g.d.d.c
– g.d.d.c, Commented Apr 24, 2012 at 14:43
Thanks for editting it, I was in middle of the process of trying to fix it XD. — Diosito
– Diosito, Commented Apr 24, 2012 at 14:46
Googling for "bad operand type for abs(): 'str'" gives a helpful answer on the very first result. — Steven Rumbalski
– Steven Rumbalski, Commented Apr 24, 2012 at 14:48
decrange is just a range function allowing for smaller steps, i =.01 in this case — Diosito
– Diosito, Commented Apr 24, 2012 at 14:48

larsks · Accepted Answer · 2012-04-24 14:44:02Z

5

The error you're getting seems fairly self-explanatory:

TypeError: bad operand type for abs(): 'str'

It looks like somewhere in your list you have a string value instead of a numeric value. This will work (assuming integer values):

listA.sort(key = lambda x: abs(int(x)))

...but it would be better to figure out why your list has strings in it and fix that instead.

answered Apr 24, 2012 at 14:44

larsks

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4 Comments

Diosito Over a year ago

I thought by floating codes it would convert it to values. listA.append(int(codes)) then would be the correct coding I suppose?

larsks Over a year ago

Calling float() should accomplish the same thing. And using int() vs float() depends on whether you expect integer values or floating point values.

Diosito Over a year ago

thanks for pointing this out those larsks, been working on this program for quite some time. Only programmed simple perl like 8 years ago, and taking a python course. Appreciate the assistance

larsks Over a year ago

If this answer helped out, please take a moment to mark it as accepted by clicking on the check mark to the left of the answer. Thanks!

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