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Note that each in scalar context returns the next key.

One of the things I rarely use.

each iterates over the keys of a hash, returning different values when called repeatedly.

>perl -E '%h=map{ $_ => 1 } qw( a b c d e f ); while ($k=each %h) { sa +y $k }' a c d b f e >

But the MUMPS $ORDER() function is different. Keys in MUMPS are always sorted, unlike Perl's hash keys. And keys must not be empty. $ORDER() returns the next key for the key you pass into. It does not iterate. Passing -1 as a second argument to $ORDER() returns the previous key instead of the next one. If there is no previous / next key, an empty string is returned.

KILL ^H SET ^H("D")=1 SET ^H("E")=1,^H("F")=1 S ^H("A")=1,^H("B")=1,^H("C")=1 ; ^-- ^H now contains the keys "A", "B", "C", "D", "E", "F" ; WRITE $ORDER(^H("")),! ; ^-- writes "A", the first key (in order) of ^H ; W $O(^H("C")),! ; ^-- writes "D", the next key after "C" in ^H ; W $O(^H("F")),! ; ^-- writes "", because "F" is the last key in ^H ; W $O(^H("D"),-1),! ; ^-- writes "C", the key before "D" in ^H ; W $O(^H("A"),-1),! ; ^-- writes "", because "A" is the first key in ^H ; SET K="" FOR SET K=$ORDER(^H(K)) QUIT:K="" DO .WRITE K WRITE ! ; ^-- writes "ABCDEF", all keys of ^H in order ; S K="" F S K=$O(^H(K,-1)) Q:K="" D .W K W ! ; ^-- writes "FEDCBA", all keys of ^H in reverse order (-1 passed as + second argument to $ORDER) ; S K="B" F S K=$O(^H(K)) Q:K="" Q:K="E" D .W K W ! ; ^-- writes "CD", all keys of ^H following "B" and stopping at the +end of keys or at "E", in order ; S K="B" F S K=$O(^H(K)) Q:K="" Q:K]]"E" D .W K W ! ; ^-- writes "CDE", all keys of ^H following "B" and stopping at the + end of keys or at the first key sorting after "E", in order

Actually, $ORDER() is a "new" (*cough*) function, it can handle negative and non-numeric keys. The original function used to iterate over keys was $NEXT(), and it was intended to be used only with positive integers, i.e. plain arrays or sparse arrays. It returns -1 if no more keys can be found. Unfortunately, -1 is a legal key. So if $NEXT() returns -1, you can not know if you found the last key or you just happen to have -1 as a key. $ORDER() fixes that problem, and $NEXT() is provided for legacy code from the dark ages.


Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

In reply to Re^6: The error says the value is uninitialized, but it works anyway by afoken
in thread The error says the value is uninitialized, but it works anyway by mizducky

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