I have an array with these datas:
[['1', '7', '14'], ['1', '1', '3'], ['1', '12', '3'], ['2', '3', '1'], ['1', '4', '9']]
I like to sort it (multiple):
>>> sorted(datas,key=lambda x:(x[0], x[1]))
[['1', '1', '3'], ['1', '12', '3'], ['1', '4', '9'], ['1', '7', '14'], ['2', '3', '1']]
but after sorted as it seems the 12 < 4. It should be:
[['1', '1', '3'], ['1', '4', '9'], ['1', '7', '14'], ['1', '12', '3'], ['2', '3', '1']]
Any idea? I need not natural sorting.
There is not wrong with sorted behaviour. Your data are lists of string, so it's doable.
>>> data = ['1', '12', '3', '2']
>>> sorted(data)
['1', '12', '2', '3']
If you want to sort as integer, it must be converted.
>>> sorted(data)
['1', '12', '2', '3']
>>> data = [['1', '7', '14'], ['1', '1', '3'], ['1', '12', '3'], ['2', '3', '1'], ['1', '4', '9']]
>>> sorted(data, key=lambda x: map(int, x))
[['1', '1', '3'], ['1', '4', '9'], ['1', '7', '14'], ['1', '12', '3'], ['2', '3', '1']]
Convert x[1] to int(x[1]):
sorted(d,key=lambda x:(int(x[0]), int(x[1])))
Output:
[['1', '1', '3'], ['1', '4', '9'], ['1', '7', '14'], ['1', '12', '3'], ['2', '3', '1']]
You are comparing strings, not ints. Therefor the order you get is the lexicographical order. If you convert to int first
sorted(data, key=lambda x:(int(x[0]), int(x[1])))
you will get the desired result
[['1', '1', '3'], ['1', '4', '9'], ['1', '7', '14'], ['1', '12', '3'], ['2', '3', '1']]
Currently your sort is working on tuples string values. String values are determined similarly to any other iterable. When it compares two strings, it goes character by character from left-to-right or index 0 to index n-1 where n is the length of the iterable, until it finds one character that is larger than another. so when comparing '12' and '4', it notices that '4' is greater than '1' so it finishes right there. This system of ordering is known as lexicographical order.
To see the "value" of a character (In Python, a character is just a string of length 1), just use the ord function:
>>> ord('1')
49
>>> ord('4')
52
And to validate that the string '12' is indeed less than '4' because ord('1') < ord('4'):
>>> '12' < '4'
True
If you want to sort by the integer values of the strings, you have to convert the strings to ints by using the built-in int constructor.
sorted(datas,key=lambda x: (int(x[0]), int(x[1]))
Or if you want to cleanly handle iterables of all sizes, simply use a tuple-generator for the key:
sorted(datas,key=lambda x: tuple(int(e) for e in x))
int