5

Common e-mail server software (postfix, sendmail, presumably exim but I didn't check that one) supports forwarding to programs via pipes, so this isn't esoteric at all. Ticketing systems such as Redmine and mailing list managers such as GNU Mailman use it all the time. If you prefer not to run your own e-mail server, you can programmatically access ...


4

So why do no major languages support this relationship? It is supported as a function, e.g. in Java List<Key> keysWithValue(Map<Key, Value> map, Value value) { return map.entrySet() .stream() .filter(e -> e.getValue().equals(value)) .map(Map.Entry::getKey) .collect(Collectors.toList()); } or in C# List&...


4

C doesn't offer custom namespaces as C++ does, but it's untrue that C doesn't have namespaces at all. Functions and structures are in different namespaces: #include <stdio.h> void Test ( ) { printf("Hello World\n"); } struct Test { int field1; int field2; }; int main ( ) { struct Test t = { 0, 1 }; Test(); return 0; } When ...


3

it's one that is supported pretty commonly in database languages like SQL You should read the fine print. Doing SELECT key WHERE value = ${val} when value is not indexed is really slow because it involves a sequential scan (linear search). To have efficient lookup in both directions, you need two indexes, i.e. two data structures. Likewise, with two-ways ...


2

In a typical RDBMS the row data lives in a separate area of storage called the heap. The B-tree is just an index pointing into the heap. It is straightforward to construct multiple indexes pointing into the same heap, on an arbitrarily determined key (you can even combine fields or apply functions to them to generate a key). There is a special-case where the ...


1

The data in a table can be ordered (this is called a clustered index) but obviously you can only have one sort order. Further indices will not reorder the data, but also they do not contain the data, only the order of rows. If the database does not have an index for the desired ORDER BY clause, it will have to build one on the fly.


1

Noone here can tell you if any database works like this, but I am pretty sure in most cases this is quite simple: For any field or combination of fields where an index was created beforehand, this index is utilized whenever the ORDER_BY clause contains the related fields. That index could be implemented as a B-tree. For any other field (or combination of ...


1

The solution by Jonathan Eunice is pretty clean and easy to follow. When constructing the list of parents, I'd slice off the parent information from the value side of the parent dictionary. Instead of this: # contstruct list of parents parents = defaultdict(list) for p in people: parents[p[2]].append(p) show_val("parents", parents) I'd have this: # ...


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