list of tuples with dynamic change in position

Ulrich Eckhardt eckhardt at satorlaser.com
Tue Sep 7 10:16:33 CEST 2010


sajuptpm wrote:
> I have a list of tuples l = [((cpu_util,mem_util),(disk_util)),
> ((cpu_util,mem_util),(disk_util))]
> ie, l = [((30,50),(70)), ((50,20),(20))]
> 
> l.sort(key=lambda x:(-x[0][0], x[1][0]))
> # sorting cpu_util asc and disk_util desc

One thing here: Without knowing what special meaning the indices have, this
code is impossible to understand. In my opinion, that code should rather be

  l.sort(key=lambda x: (-x.cpu_util, x.disk_util))

You could then save the comment, which btw may or may not describe the
actual code.

> suppose i changed order that is l = [((mem_util,cpu_util),
> (disk_util)), ((mem_util,cpu_util),(disk_util))]
> So i have to change the sort code to l.sort(key=lambda x:(-x[0][1],
> x[1][0])) # sorting cpu_util asc and disk_util desc
>
> I want to use same (common) sort code, that must work even if i
> changed tuple order.

You don't have to use a lambda function. You can as well define the sorting
order in the same place of your code where you define the order inside the
elements, that way you would only have to adjust the sorting in one place.

Otherwise, you will have to embed the order of the tuple inside the tuple or
the containing list. One approach would be to have a dictionary (which has
no order), or you use a separate type instead:

  class record(object):
      pass

  r = record()
  r.cpu_util = 12
  r.disk_util = 42
  l.append(r)

However, this basically all boils down to either "don't use the sorting
(dict)" or "keep records sorted", so it doesn't really answer your
question. However, I'm afraid there is no answer to your question as it
stands. Maybe I could help you better if you explained why the order
changes etc, because normally I don't deal with data that has such a
volatile meaning, I rather normalize it on input and then use it in the
same way afterwards.

Uli

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