Question

This question is in relation to another question asked here:
Sorting 1M records

I have since figured out the problem I was having with sorting. I was sorting items from a dictionary into a list every time I updated the data. I have since realized that a lot of the power of Python’s sort resides in the fact that it sorts data more quickly that is already partially sorted.

So, here is the question. Suppose I have the following as a sample set:

self.sorted_records = [(1, 1234567890), (20, 1245678903), 
                       (40, 1256789034), (70, 1278903456)]

t[1] of each tuple in the list is a unique id. Now I want to update this list with the follwoing:

updated_records = {1245678903:45, 1278903456:76}

What is the fastest way for me to do so ending up with

self.sorted_records = [(1, 1234567890), (45, 1245678903),
                       (40, 1256789034), (76, 1278903456)]

Currently I am doing something like this:

updated_keys = updated_records.keys()
for i, record in enumerate(self.sorted_data):
    if record[1] in updated_keys:
        updated_keys.remove(record[1])
        self.sorted_data[i] = (updated_records[record[1]], record[1])

But I am sure there is a faster, more elegant solution out there.

Any help?

* edit
It turns out I used bad exaples for the ids since they end up in sorted order when I do my update. I am actually interested in t[0] being in sorted order. After I do the update I was intending on resorting with the updated data, but it looks like bisect might be the ticket to insert in sorted order.
end edit *

Answer 1

Since apparently you don’t care about the ending value of self.sorted_records actually being sorted (you have values in order 1, 45, 20, 76 — that’s NOT sorted!-), AND you only appear to care about IDs in updated_records that are also in self.sorted_data, a listcomp (with side effects if you want to change the updated_record on the fly) would serve you well, i.e.:

self.sorted_data = [(updated_records.pop(recid, value), recid) 
                    for (value, recid) in self.sorted_data]

the .pop call removes from updated_records the keys (and corresponding values) that are ending up in the new self.sorted_data (and the “previous value for that recid“, value, is supplied as the 2nd argument to pop to ensure no change where a recid is NOT in updated_record); this leaves in updated_record the “new” stuff so you can e.g append it to self.sorted_data before re-sorting, i.e I suspect you want to continue with something like

self.sorted_data.extend(value, recid 
                        for recid, value in updated_records.iteritems())
self.sorted_data.sort()

though this part DOES go beyond the question you’re actually asking (and I’m giving it only because I’ve seen your previous questions;-).