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On Fri, Feb 13, 2015 at 02:46:45AM +1100, Chris Angelico wrote:
Imagine if two people independently build shopping lists
Sorry, was that shopping *lists* or shopping *dicts*?
- "this is the stuff we need" - and then combine them. You'd describe that as "your list and my list", or "your list plus my list" (but not "your list or my list"; English and maths tend to get "and" and "or" backward to each other in a lot of ways), and the resulting list would basically be set union of the originals. If you have room on one of them, you could go through the other and add all the entries that aren't already present; otherwise, you grab a fresh sheet of paper, and start merging the lists. (If you're smart, you'll group similar items together as you merge. That's where the analogy breaks down, though.) It makes fine sense to take two shopping lists and combine them into a new one, discarding any duplicates.
Why would you discard duplicates? If you need 2 loaves of bread, and I need 1 loaf of bread, and the merged shopping list has anything less than 3 loaves of bread, one of us is going to miss out. -- Steve