Erasing From a map

[EvilOldGit]

If I have a map<double,double>, how do I delete the item whose
"second" value is X ?

[Mark P]

Ev********@googlemail.com wrote:

If I have a map<double,double>, how do I delete the item whose
"second" value is X ?

The same way you'd delete any item from a map-- call erase on either the
key of or an iterator to the item. I suspect that what you mean to ask
is how to _find_ an item by its second value. The simple answer is that
there's no especially good way to do this with std::map short of
iterating through the entire map. If that's not good enough then you'll
need a better data structure.

[fcvcnet]

Mark P 写�:

Ev********@googlemail.com wrote:

>If I have a map<double,double>, how do I delete the item whose
"second" value is X ?

The same way you'd delete any item from a map-- call erase on either the
key of or an iterator to the item. I suspect that what you mean to ask
is how to _find_ an item by its second value. The simple answer is that
there's no especially good way to do this with std::map short of
iterating through the entire map. If that's not good enough then you'll
need a better data structure.

Can the boost library do this work?

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Thank this newsgroup very much! :)
fc*****@163.com

[Jim Langston]

<Ev********@googlemail.comwrote in message
news:11*********************@b75g2000hsg.googlegro ups.com...

If I have a map<double,double>, how do I delete the item whose
"second" value is X ?

I've always wanted a map with more than one index, but it's not in the
standard. So, with a standard map: iterate though the members til you find
the one with the second value of x, delete it. There may be an algorithm to
find it easier, but I don't generally use standard algorithms so can't tell
you. I would suspect if it existed it would have "find" somewhere in it.

[Michael Oswald]

fcvcnet wrote:

Mark P 写�:

>short of iterating through the entire map. If that's not good enough
then you'll need a better data structure.

Can the boost library do this work?

Yup. Look at multi_index.
lg,
Michael