Question

I have a list which contains more than 75 thousand object. To search item from list currently I am using following code.

from nd in this.m_ListNodes
where
   nd.Label == SearchValue.ToString()
   select
   nd;

Is this code is efficient?

Answer 1

How often do you need to search the same list? If you’re only searching once, you might as well do a straight linear search – although you can make your current code slightly more efficient by calling SearchValue.ToString() once before the query.

If you’re going to perform this search on the same list multiple times, you should either build a Lookup or a Dictionary:

var lookup = m_ListNodes.ToLookup(nd => nd.Label);

or

var dictionary = m_ListNodes.ToDictionary(nd => nd.Label);

Use a dictionary if there’s exactly one entry per label; use a lookup if there may be multiple matches.

To use these, for a lookup:

var results = lookup[SearchValue.ToString()];
// results will now contain all the matching results

or for a dictionary:

WhateverType result;
if (dictionary.TryGetValue(SearchValue.ToString(), out result))
{
    // Result found, stored in the result variable
}
else
{
    // No such item
}