CODEWITHSUNDEEP
python
urschrei
urschrei

Reputation: 26859

Most efficient way to remove non-numeric list entries

I'm looking to 'clean' a list by excluding any items which contain characters other than 0-9, and wondering if there's a more efficient way than e.g.

import re
invalid = re.compile('[^0-9]')    
ls = ['1a', 'b3', '1']
cleaned = [i for i in ls if not invalid.search(i)]
print cleaned
>> ['1']

As I'm going to be operating on large-ish lists (5k items) of long strings (15 chars).

Upvotes: 14

Views: 32474

Answers (3)

Franck Dernoncourt
Franck Dernoncourt

Reputation: 83197

In case one wants to keep both integers and floats in the output:

def is_float(string):
    try:
        float(string)
        return True
    except:
        return False

example_list = ['text', 'another text', '1', '2.980', '3']
output = [a for a in example_list if is_float(a)]
print(output)      
# Output is: ['1', '2.980', '3']

Alternatively, one can use filter, as eumiro suggested:

output = list(filter(is_float, example_list))
print(output)
# Output is: ['1', '2.980', '3']

Credit: is_float() comes from this answer by Saullo G. P. Castro.

Upvotes: -1

Forhadul Islam
Forhadul Islam

Reputation: 1237

You can use isnumeric function. It checks whether the string consists of only numeric characters. This method is present only on unicode objects. It won't work with integer or float values

myList = ['text', 'another text', '1', '2.980', '3']
output = [ a for a in myList if a.isnumeric() ]
print( output )      
# Output is : ['1', '3']

Ref: https://www.tutorialspoint.com/python/string_isnumeric.htm

Upvotes: 2

MattH
MattH

Reputation: 38247

Anything wrong with the string method isdigit ?

>>> ls = ['1a', 'b3', '1']
>>> cleaned = [ x for x in ls if x.isdigit() ]
>>> cleaned
['1']
>>>

Upvotes: 18

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