Mapping two set of values in C++

Question

My sincere apologies for such a naive question. I know this is simple. But nothing comes to my mind now.

I am using C++. I'm a bit concerned about efficiency since this is targeted for an embedded hardware with very less processing power and RAM.

I have 2 integer arrays with 50 members local to a function. I need to determine what is the corresponding number in the second array when an element in the first array is specified and vice versa. I have the information that the element provided to me for look-up belongs to which array i.e. array 1 or array 2.

Ex : Array1 => 500 200 1000 300 .....

 Array2 => 250 170 500  400 .....

Input 500 , Output will be 250

Input 400 , Output will be 300

input 200 , Output will be 170 and so on

I think an array look-up will be least efficient. Is stl::map the best option or do i have to look for any efficient search algorithms? I would like to know if you have to do this, which option you will be choosing.

Any thoughts?

With only 50 items, efficiency is never a problem. – Sergey Kalinichenko Jan 04 '13 at 05:35 — Sergey Kalinichenko, Jan 04 '13 at 05:35
If arrays are static, should index be enough? – billz Jan 04 '13 at 05:43 — billz, Jan 04 '13 at 05:43

score 4 · Accepted Answer · edited May 23 '17 at 11:50

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You can use std::map for readability and a little efficiency as well, though in your case efficiency is of small matter

std::map<int,int> mapping;
.... //populate 
cout <<mapping[200]; //170

This is only 1 way (Array 1 -> Array 2) though. Im not sure if any easier way to do the other way, but create a second map.

To support reverse lookup, or going from (Array 2 -> Array 1), Reverse map lookup suggests using Boost.Bimap

edited May 23 '17 at 11:50

Community

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answered Jan 04 '13 at 05:33

Karthik T

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If the arrays are literally static, then a `switch`/`case` statement will probably be fastest. Otherwise, `std::map` is probably best. – David Schwartz Jan 04 '13 at 06:01
@DavidSchwartz : Oh, yes. I completely missed out switch case option. I know it will produce a lengthy weird function, but still in terms of efficiency it will be my best bet. – NeonGlow Jan 04 '13 at 06:15

score 1 · Answer 2 · answered Jan 04 '13 at 07:19

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According to me there are 2 ways of doing it both have already been suggested;

put the both arrays in a map as key pair value and traverse map to find the corresponding value or key.
Traverse the array for which the input is there and calculate the index. Get the value for that index int he other array.

I would go for the second solution as it easier. Moreover with only 50 elements in a static array you don't need to worry about performance.

answered Jan 04 '13 at 07:19

spanky

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+1 Added. IMHO The switch case option suggested by David Schwartz is most efficient. – NeonGlow Jan 04 '13 at 10:55
Point taken.Switch case is the most efficient.But with 50 elements you will end with a huge function. – spanky Jan 04 '13 at 11:09

Mapping two set of values in C++

2 Answers2