Re: map or set for handling struct with a key?

Mark P <>
Wed, 08 Aug 2007 20:26:22 GMT
Digital Puer wrote:

On Aug 8, 12:53 pm, "Victor Bazarov" <> wrote:

Digital Puer wrote:

Hi, I was wondering whether to use a map or a set for
my purposes.
I am reading rows from a database and am populating a
struct (or class) for each row. It has a key and ancillary
data, e.g.:
struct Foo {
 int key;
 float data1;
 int data2;
 string data3;
Now I want to keep all the rows in either a map or a set.
If I use a set, I can keep the struct the way it is; the only
thing I need is to provide a comparison function for the set
so that the ordering is based on the key.
On the other hand, if I use a map, I am inclined to break
the key out and use the key as the first part in the map,
struct Foo {
 float data1;
 int data2;
 string data3;
map<int, Foo> mydata;
Which approach is preferable for the following cases:
1. My only operations on the data structure are to iterate
over it and to use find().
2. I will iterate over as well as update the data.

If you don't update the keys, ever, then you're better off with
a sorted vector/deque.


Please explain why a sorted vector or deque is better than
map or set. A find() will be O(lg n) with any of them.

In general, it will be faster to read all of the data into a vector and
sort it once rather than reading the data into a set or map and sorting
"online". A vector will also use less space in general.

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