Is there a way to output the numbers, that are in string format, only from a python list?

Question

Simple question:

How to only extract integers (no floats) from a list of strings?

Like this:

list_1 = [['50', 'ALA', 'A', '53', '5', '4'], ['55', 'GLY', 'A', '60', '1', '6'], ['67', 'ILE', 'A', '71', '5', '5']]

To this:

list_1 = [['50', '53', '5', '4'], ['55', '60', '1', '6'], ['67', '71', '5', '5']]

Thank you.

Answer 1

You can use the str.isdigit method.

>>> list_1 = ['50', 'ALA', 'A', '53', '5', 'N', '4']
>>> list_1 = [x for x in list_1 if x.isdigit()]
>>> list_1
['50', '53', '5', '4']

Note that this will not work for floating point representations of numbers.

>>> '650.43'.isdigit()
False

If you want to filter these as well, write a traditional loop.

>>> list_1 = ['50', '650.43', 'test']
>>> result = []
>>> for x in list_1:
...     try:
...         float(x)
...         result.append(x)
...     except ValueError:
...         pass
... 
>>> result
['50', '650.43']

Answer 2

It can be done by this piece of code, it will manage floats too, handling errors and exceptions.

Loop can be converted into comprehension for more Pythonic way.

def isfloat(value):
  try:
    float(value)
    return True
  except:
    return False

v = ['50', 'ALA', 'A', '53', '5', 'N', '4']
result = []
for x, i in enumerate(map(isfloat, v)):
    if i is True:
    result.append(v[x])

print result # [50, 53, 5, 4]

Answer 3

You can try this:

list_1 = ['50', 'ALA', 'A', '53', '5', 'N', '4']

digits = []
for item in list_1:
    for subitem in item.split():
        if(subitem.isdigit()):
            digits.append(subitem)
print(digits) 

Output:

['50', '53', '5', '4']

Answer 4

You Can do this

list_1 = ['50', 'ALA', 'A', '53', '5', 'N', '4']
list_2 =[]
for i in range(len(list_1)):
    if list_1[i].isnumeric():
        list_2.append(list_1[i])
print(list_2)