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So I have this list here:

[['Afghanistan', '2.66171813', '7.460143566', '0.490880072', '52.33952713', '0.427010864', '-0.106340349', '0.261178523'], ['Albania', '4.639548302', '9.373718262', '0.637698293', '69.05165863', '0.74961102', '-0.035140377', '0.457737535'], ['Algeria', '5.248912334', '9.540244102', '0.806753874', '65.69918823', '0.436670482', '-0.194670126', ''], ['Argentina', '6.039330006', '9.843519211', '0.906699121', '67.53870392', '0.831966162', '-0.186299905', '0.305430293'], ['Armenia', '4.287736416', '9.034710884', '0.697924912', '65.12568665', '0.613697052', '-0.132166177', '0.246900991'], ['Australia', '7.25703764', '10.71182728', '0.949957848', '72.78334045', '0.910550177', '0.301693261', '0.45340696']]

My aim is to loop through the list of lists and convert number string values to integers.

I tried

for li in main_li: for element in li: if element == li[0]: continue else: element = int(element)

My problem is how can I get this back into the same list format I had above without the numbers being strings.

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  • your string numbers are float not integer , you want them to be round or something? Commented Feb 22, 2019 at 6:20
  • what's your desired output ? Commented Feb 22, 2019 at 6:21
  • Your code does not modify the original list. Because you are assigning a new value to a loop variable not to an index in the list. Commented Feb 22, 2019 at 6:22
  • You have an empty string ‘‘ at the end of the third sublist with ‘Algeria’. I suppose it shouldn’t be there. Commented Feb 22, 2019 at 9:17

6 Answers 6

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2

You can do it by making a small change in your code

for li in main_li: for i in range(1,len(li)): try: li[i] = int(li[i]) except ValueError: pass
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Please don't encourage the catch-all except. It often ends badly. stackoverflow.com/questions/14797375/…
1

You shouldn't (not saying it's not possible) change list values while you loop over them. You'll have to create a new list. Fortunately, you can do it very easily with a small modification to your original code:

newlist = [] for li in main_li: newli = [] for element in li: if element == li[0]: newli.append(element) else: try: newli.append(int(float(element))) except Exception as e: newli.append(0) # This is added because not everything in your list can be converted to int. newlist.append(newli)

newlist will be your modified list of lists.

Alternatively, you can use list comprehension:

newlist = [[p[0]] + [int(float(x)) for x in p[1:]] for p in main_li]

Note how this requires all of your string to be correctly formatted.

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1

Your list elements are float so you can only convert them to float:

import re pattern = re.compile('[-+]?\d+(\.\d+)?') # a pattern for all number types new_list = [] for nest in l: temp_list = [] for val in nest: if bool(pattern.match(val)): #check if the element is a number temp_list.append(float(val)) continue temp_list.append(val) new_list.append(temp_list) print(new_list) [['Afghanistan', 2.66171813, 7.460143566, 0.490880072, 52.33952713, 0.427010864, -0.106340349, 0.261178523], ['Albania', 4.639548302, 9.373718262, 0.637698293, 69.05165863, 0.74961102, -0.035140377, 0.457737535], ['Algeria', 5.248912334, 9.540244102, 0.806753874, 65.69918823, 0.436670482, -0.194670126, ''], ['Argentina', 6.039330006, 9.843519211, 0.906699121, 67.53870392, 0.831966162, -0.186299905, 0.305430293], ['Armenia', 4.287736416, 9.034710884, 0.697924912, 65.12568665, 0.613697052, -0.132166177, 0.246900991], ['Australia', 7.25703764, 10.71182728, 0.949957848, 72.78334045, 0.910550177, 0.301693261, 0.45340696]]
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Your approach doesn't cover negative numbers and also broke the list format.
In Python, "inf", "infinity", "NaN" and exponential notation ("1.23E4") are all strings that can be converted to floating values. Those cases are niet caught by your regex...
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Simply just convert those elements that are convertible to float and change them in current list with iterating through list index:

for i in range(len(main_li)): for j in range(len(main_li[i])): try: main_li[i][j] = float(main_li[i][j]) except ValueError: continue li # [['Afghanistan', 2.66171813, 7.460143566, 0.490880072, 52.33952713, 0.427010864, -0.106340349, 0.261178523], ['Albania', 4.639548302, 9.373718262, 0.637698293, 69.05165863, 0.74961102, -0.035140377, 0.457737535], ['Algeria', 5.248912334, 9.540244102, 0.806753874, 65.69918823, 0.436670482, -0.194670126, ''], ['Argentina', 6.039330006, 9.843519211, 0.906699121, 67.53870392, 0.831966162, -0.186299905, 0.305430293], ['Armenia', 4.287736416, 9.034710884, 0.697924912, 65.12568665, 0.613697052, -0.132166177, 0.246900991], ['Australia', 7.25703764, 10.71182728, 0.949957848, 72.78334045, 0.910550177, 0.301693261, 0.45340696]]
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0

Most of the answers assume a fixed level of nesting (list of lists). You could (if applicable) use the following code, which uses recursion of handle deeper nested lists (lists of lists of lists, etc).

def nested_str_to_float(value): """ Converts an string to float. Value may be a single value, a list or even a nested list. If value is a (nested) list, all values in the (nested) list are evaluated to floats wherever possible. Args: value: single value of any type or a list Returns: a copy of value with all float-convertible items converted to float """ # Test if value is a list, if so, recursively call nested_str_to_float if isinstance(value, list): return [nested_str_to_float(item) for item in value] # Try to convert to float; if possible, return float, else return value try: return float(value) except ValueError: return value

By the way, check this SO answer to see what Python considers floats...

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0

You can use a star unpacking in a listcomp:

l = [['A', '1.1', '1.2'], ['B', '2.1', '2.2']] [[i, *map(float, j)] for i, *j in l] # [['A', 1.1, 1.2], ['B', 2.1, 2.2]]
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