sorting a list of list

[james_027]

hi,

are there available library or pythonic algorithm for sorting a list
of list depending on the index of the list inside the list of my
choice?

d_list = [
['a', 1, 9],
['b', 2, 8],
['c', 3, 7],
['d', 4, 6],
['e', 5, 5],
]

Thanks
james

[Tim Chase]

are there available library or pythonic algorithm for sorting a list

of list depending on the index of the list inside the list of my
choice?

The built-in sorted() function and the sort() method on various
collections take an optional "key=function" keyword paramater
with which you can pass a function (lambdas are convenient) to
extract the bit on which you want to compare:

>>d_list = [

.... ['a', 1, 9],
.... ['b', 2, 8],
.... ['c', 3, 7],
.... ['d', 4, 6],
.... ['e', 5, 5],
.... ]

>>print sorted.__doc__

sorted(iterable, cmp=None, key=None, reverse=False) --new
sorted list

>>sorted(d_list, key=lambda x: x[2]) # sort by the 3rd item

[['e', 5, 5], ['d', 4, 6], ['c', 3, 7], ['b', 2, 8], ['a', 1, 9]]

>>sorted(d_list, key=lambda x: x[1]) # sort by the 2nd item

[['a', 1, 9], ['b', 2, 8], ['c', 3, 7], ['d', 4, 6], ['e', 5, 5]]

>>sorted(d_list, key=lambda x: x[0]) # sort by the 1st item

[['a', 1, 9], ['b', 2, 8], ['c', 3, 7], ['d', 4, 6], ['e', 5, 5]]

-tkc

[Matt Nordhoff]

Tim Chase wrote:

>are there available library or pythonic algorithm for sorting a list
of list depending on the index of the list inside the list of my
choice?

The built-in sorted() function and the sort() method on various
collections take an optional "key=function" keyword paramater
with which you can pass a function (lambdas are convenient) to
extract the bit on which you want to compare:

>>>d_list = [

... ['a', 1, 9],
... ['b', 2, 8],
... ['c', 3, 7],
... ['d', 4, 6],
... ['e', 5, 5],
... ]

>>>print sorted.__doc__

sorted(iterable, cmp=None, key=None, reverse=False) --new
sorted list

>>>sorted(d_list, key=lambda x: x[2]) # sort by the 3rd item

[['e', 5, 5], ['d', 4, 6], ['c', 3, 7], ['b', 2, 8], ['a', 1, 9]]

>>>sorted(d_list, key=lambda x: x[1]) # sort by the 2nd item

[['a', 1, 9], ['b', 2, 8], ['c', 3, 7], ['d', 4, 6], ['e', 5, 5]]

>>>sorted(d_list, key=lambda x: x[0]) # sort by the 1st item

[['a', 1, 9], ['b', 2, 8], ['c', 3, 7], ['d', 4, 6], ['e', 5, 5]]

Not to be too complicated, but there are functions that return a
callable that is faster than a lambda.

>>import operator

Then, instead of "lambda x: x[2]" use "operator.itemgetter(2)" and
instead of "lambda x: x.foo" use "operator.attrgetter('foo')".
--