Sorting on multiple values, some ascending, some descending

[dwelden]

I have successfully used the sort lambda construct described in
http://mail.python.org/pipermail/pyt...il/377443.html.
However, how do I take it one step further such that some values can be
sorted ascending and others descending? Easy enough if the sort values
are numeric (just negate the value), but what about text?

Is the only option to define an external sorting function to loop
through the list and perform the comparisons one value at a time?

[Peter Otten]

Neil Cerutti wrote:

Another trick is to factor the key application out of the sort.
This may be a good idea if when you want to minimize the number
of times your key function is called.

The idea is to mangle the list temporarily so you can use an
unkeyed sort, and then unmangle the sorted data. Here's a silly
example using a phone directory that's not stored in a format
that's easy to sort.

No need to jump through these hoops; list.sort(key=k eyfunc) calls keyfunc()
exactly once per list item:

>>from random import shuffle
items = range(-5, 10)
shuffle(items )
count = 0
def key(value):

.... global count
.... count += 1
.... return abs(value)
....

>>items.sort(ke y=key)
count

15

Peter

[Neil Cerutti]

On 2007-01-04, Peter Otten <__*******@web. dewrote:

Neil Cerutti wrote:

>Another trick is to factor the key application out of the
sort. This may be a good idea if when you want to minimize the
number of times your key function is called.

The idea is to mangle the list temporarily so you can use an
unkeyed sort, and then unmangle the sorted data. Here's a
silly example using a phone directory that's not stored in a
format that's easy to sort.

No need to jump through these hoops; list.sort(key=k eyfunc)
calls keyfunc() exactly once per list item:

>>>from random import shuffle
items = range(-5, 10)
shuffle(item s)
count = 0
def key(value):

... global count
... count += 1
... return abs(value)
...

>>>items.sort(k ey=key)
count

15

Thanks for the correction! That's very useful information.

--
Neil Cerutti