Python - TypeError: float() argument must be a string or a number, not 'list

Question

Python newbie here. I am trying to operate on lists which contain floating point numbers. avg is a list parameter that is returned from a different method. However, when I tried doing the following, it throws me an error that float() should have a string or a number and not a list. avg1 should contain a copy of the lists with float-type numbers instead of lists right? I tried a few edits I read on other posts with similar titles, but couldn't solve this. Just starting out so kindly tell me where I am going wrong.

def movingavg(EMA,avg):     
    EMA=[]
    avg1 = [float(i) for i in avg]
    EMA[:3] = avg1[:3]
    for i,j in zip(EMA[2:],avg1[3:]):
        a =float(i)*0.67 + float(j)*0.33
        EMA.append(a)
    return EMA

The error that I get is as follows :

avg1 = [float(i) for i in avg]
TypeError: float() argument must be a string or a number, not 'list'

Using Python 3.4

Please post an example of what avg looks like. Seems as if it is a list of lists or sth alike. — jbndlr
– jbndlr, Commented Sep 7, 2016 at 11:20
@jbndlr it is a list with numbers taken from a column in a pandas dataframe. [[12312188.0], [6055962.0], [2753511.0], [3216789.0], [3554074.0], [4638837.0], [7064825.0], [4162710.0], [3262018.0], [3913376.0], [3945705.0]] I have included a few values out of the many. — Sastry Gosukonda
– Sastry Gosukonda, Commented Sep 7, 2016 at 11:33
See, you got a list of lists there. Change your float-cast to float(i[0]) if it's always in this shape. — jbndlr
– jbndlr, Commented Sep 7, 2016 at 11:35

Dinesh Pundkar · Accepted Answer · 2016-09-07 11:54:02Z

2

Instead of avg1 = [float(i) for i in avg] use below code.

avg1 = []
for i in avg:
    for j in i:
        avg1.append(float(j))

or can use below list comprehension.

avg1 = [float(i)  for val in avg for i in val]

edited Sep 7, 2016 at 11:54

answered Sep 7, 2016 at 11:41

Dinesh Pundkar

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11 Comments

Dartmouth Over a year ago

Using a list comprehension would be a lot more concise for this.

Dinesh Pundkar Over a year ago

I am writing it. Just posted answer. Will edit in minute. :)

Dartmouth Over a year ago

The result of the list comprehension will produce a single list rather than keeping the data structure of the OP.

Dinesh Pundkar Over a year ago

Yups. I think the code which is executed after this line of code, requires single list and not list of list. That's why I created single list.

Dinesh Pundkar Over a year ago

Initially I have written comprehension similar like yours. But then checked the code and changed it.

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Aman Jaiswal · Accepted Answer · 2016-09-07 11:34:01Z

0

Please check return type of avg I think it's return type is list's of list.

answered Sep 7, 2016 at 11:34

Aman Jaiswal

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2 Comments

Sastry Gosukonda Over a year ago

I did, and you're right, it's a list of lists. But how do I cast it to float for use?

Dartmouth Over a year ago

@AmanJaiswal that isn't actually using the map function though, that's just an embedded list comprehension.

Dartmouth · Accepted Answer · 2016-09-07 11:41:39Z

0

To convert a list of lists to float, you need to use two list comprehensions, like this:

avg1 = [[float(i) for i in val] for val in avg]

answered Sep 7, 2016 at 11:41

Dartmouth

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1 Comment

Dinesh Pundkar Over a year ago

This will result again in list of list.

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