Hi all,
Say I have two maps m1 and m2. Both have key as std::string and value
as long.
m1 could hold entries like
"abc" 123
"def" 456
m2 could have entries like
"abc" 789
"hij" 111
I want to show the union of these results like this
"abc" 123 789
"def" 456 0
"hij" 0 111
One way to deal with it would be to form a map<string, vector<long> >,
then loop over m1 and fill it, then loop over m2 and if there is some
existent entry for a key then push_back the value in vector. Doesn't
seem very clean to me. I am sure there might be better approaches. Can
you suggest some ?
Should I have something like map<string, long[2]> instead of m1 and m2
in the first place ?
Thanks. 2 1464
Old Monk wrote: Hi all,
Say I have two maps m1 and m2. Both have key as std::string and value as long.
m1 could hold entries like "abc" 123 "def" 456
m2 could have entries like "abc" 789 "hij" 111
I want to show the union of these results like this
"abc" 123 789 "def" 456 0 "hij" 0 111
One way to deal with it would be to form a map<string, vector<long> >, then loop over m1 and fill it, then loop over m2 and if there is some existent entry for a key then push_back the value in vector. Doesn't seem very clean to me.
It's probably the way I would do it (the lazy way)
I am sure there might be better approaches. Can you suggest some ?
The idea of adapting the idea behind merge sort comes to my mind.
initialize top_first with the first entry in map1
inttialize top_scnd with the first entry in map2
while top_first && top_secnd {
if *top_first == *top_secnd
build new entry combining *top_first and *top_scnd, add to map3
advance top_first
advance top_secnd
else
if *top_first < *top_scnd
build new entry from *top_first, add to map3
advance top_first
else
build new entry from *top_secnd, add to map3
advance top_secnd
}
// while loop finished, either top_first or top_secnd
// or both have reached the end of their map. But one of
// the maps may still contain eintries, add them to the
// result
while top_first {
build new entry from *top_first, add to map3
advance top_first
}
while top_secnd {
build new entry from *top_secnd, add to map3
advance top_secnd
}
Something like that. Might be faster since no search through
the maps is involved. Should I have something like map<string, long[2]> instead of m1 and m2 in the first place ?
long[2] *would* be fine. But since plain vanilla arrays don't satisfy the
copy and assignment requirements imposed by the standard containers, it
cannot be used. But you could do:
struct Entry
{
long Value1;
long Value2;
}
map< string, Entry >
If that is ok for m1 and m2 is only you to decide. I wouldn't do it. The
operation you want to do is not a standard one, so why blow up the input
maps needlessly. For the result you can either use
map< string, vector< long > >
or
map< string, Entry >
it doesn't make much of a difference (in this specific case. If you
sometimes plan to merge 3 input maps, then things change. But for the
moment ...)
--
Karl Heinz Buchegger kb******@gascad .at
In article <41************ ***@gascad.at>,
Karl Heinz Buchegger <kb******@gasca d.at> wrote: Old Monk wrote: Hi all,
Say I have two maps m1 and m2. Both have key as std::string and value as long.
m1 could hold entries like "abc" 123 "def" 456
m2 could have entries like "abc" 789 "hij" 111
I want to show the union of these results like this
"abc" 123 789 "def" 456 0 "hij" 0 111
One way to deal with it would be to form a map<string, vector<long> >, then loop over m1 and fill it, then loop over m2 and if there is some existent entry for a key then push_back the value in vector. Doesn't seem very clean to me.
It's probably the way I would do it (the lazy way)
I am sure there might be better approaches. Can you suggest some ?
The idea of adapting the idea behind merge sort comes to my mind.
initialize top_first with the first entry in map1 inttialize top_scnd with the first entry in map2
while top_first && top_secnd {
if *top_first == *top_secnd build new entry combining *top_first and *top_scnd, add to map3 advance top_first advance top_secnd
else if *top_first < *top_scnd build new entry from *top_first, add to map3 advance top_first else build new entry from *top_secnd, add to map3 advance top_secnd } // while loop finished, either top_first or top_secnd // or both have reached the end of their map. But one of // the maps may still contain eintries, add them to the // result while top_first { build new entry from *top_first, add to map3 advance top_first }
while top_secnd { build new entry from *top_secnd, add to map3 advance top_secnd }
Something like that. Might be faster since no search through the maps is involved.
Should I have something like map<string, long[2]> instead of m1 and m2 in the first place ?
long[2] *would* be fine. But since plain vanilla arrays don't satisfy the copy and assignment requirements imposed by the standard containers, it cannot be used. But you could do:
struct Entry { long Value1; long Value2; }
map< string, Entry >
If that is ok for m1 and m2 is only you to decide. I wouldn't do it. The operation you want to do is not a standard one, so why blow up the input maps needlessly. For the result you can either use
map< string, vector< long > >
or map< string, Entry >
it doesn't make much of a difference (in this specific case. If you sometimes plan to merge 3 input maps, then things change. But for the moment ...)
Another option would be to use std::pair, as in:
map< string, pair< long, long > >; This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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