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Jacky
Jacky

Reputation: 285

How to remove all integer values from a list in python

I am just a beginner in python and I want to know is it possible to remove all the integer values from a list? For example the document goes like

['1','introduction','to','molecular','8','the','learning','module','5']

After the removal I want the document to look like:

['introduction','to','molecular','the','learning','module']

Upvotes: 20

Views: 84889

Answers (8)

Daniel Stutzbach
Daniel Stutzbach

Reputation: 76667

To remove all integers, do this:

no_integers = [x for x in mylist if not isinstance(x, int)]

However, your example list does not actually contain integers. It contains only strings, some of which are composed only of digits. To filter those out, do the following:

no_integers = [x for x in mylist if not (x.isdigit() 
                                         or x[0] == '-' and x[1:].isdigit())]

Alternately:

is_integer = lambda s: s.isdigit() or (s[0] == '-' and s[1:].isdigit())
no_integers = filter(is_integer, mylist)

Upvotes: 42

buddu
buddu

Reputation: 51

To remove all integers from the list 

ls = ['1','introduction','to','molecular','8','the','learning','module','5']
ls_alpha = [i for i in ls if not i.isdigit()]
print(ls_alpha)

Upvotes: 2

user1877394
user1877394

Reputation:

You can use the filter built-in to get a filtered copy of a list.

>>> the_list = ['1','introduction','to','molecular',-8,'the','learning','module',5L]
>>> the_list = filter(lambda s: not str(s).lstrip('-').isdigit(), the_list)
>>> the_list
['introduction', 'to', 'molecular', 'the', 'learning', 'module']

The above can handle a variety of objects by using explicit type conversion. Since nearly every Python object can be legally converted to a string, here filter takes a str-converted copy for each member of the_list, and checks to see if the string (minus any leading '-' character) is a numerical digit. If it is, the member is excluded from the returned copy.

The built-in functions are very useful. They are each highly optimized for the tasks they're designed to handle, and they'll save you from reinventing solutions.

Upvotes: 0

Baltasarq
Baltasarq

Reputation: 12212

You can also use lambdas (and, obviously, recursion), to achieve that (Python 3 needed):

 isNumber = lambda s: False if ( not( s[0].isdigit() ) and s[0]!='+' and s[0]!='-' ) else isNumberBody( s[ 1:] )

 isNumberBody = lambda s: True if len( s ) == 0 else ( False if ( not( s[0].isdigit() ) and s[0]!='.' ) else isNumberBody( s[ 1:] ) )

 removeNumbers = lambda s: [] if len( s ) == 0 else ( ( [s[0]] + removeNumbers(s[1:]) ) if ( not( isInteger( s[0] ) ) ) else [] + removeNumbers( s[ 1:] ) )

 l = removeNumbers(["hello", "-1", "2", "world", "+23.45"])
 print( l )

Result (displayed from 'l') will be: ['hello', 'world']

Upvotes: 1

twneale
twneale

Reputation: 2946

I personally like filter. I think it can help keep code readable and conceptually simple if used in a judicious way:

x = ['1','introduction','to','molecular','8','the','learning','module','5'] 
x = filter(lambda i: not str.isdigit(i), x)

or

from itertools import ifilterfalse
x = ifilterfalse(str.isdigit, x)

Note the second returns an iterator.

Upvotes: 5

FT.
FT.

Reputation: 11

Please do not use this way to remove items from a list: (edited after comment by THC4k)

>>> li = ['1','introduction','to','molecular','8','the','learning','module','5']
>>> for item in li:
        if item.isdigit():
            li.remove(item)

>>> print li
['introduction', 'to', 'molecular', 'the', 'learning', 'module']

This will not work since changing a list while iterating over it will confuse the for-loop. Also, item.isdigit() will not work if the item is a string containing a negative integer, as noted by razpeitia.

Upvotes: 1

S.Lott
S.Lott

Reputation: 391854

You can do this, too:

def int_filter( someList ):
    for v in someList:
        try:
            int(v)
            continue # Skip these
        except ValueError:
            yield v # Keep these

list( int_filter( items ))

Why? Because int is better than trying to write rules or regular expressions to recognize string values that encode an integer.

Upvotes: 13

Gary Kerr
Gary Kerr

Reputation: 14420

None of the items in your list are integers. They are strings which contain only digits. So you can use the isdigit string method to filter out these items. 

items = ['1','introduction','to','molecular','8','the','learning','module','5']

new_items = [item for item in items if not item.isdigit()]

print new_items

Link to documentation: http://docs.python.org/library/stdtypes.html#str.isdigit

Upvotes: 14

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