CODEWITHSUNDEEP
c#
Moe
Moe

Reputation: 45

Iterating through a list is very slow, how to improve the performance

I have a method that iterate through a list and display the result of each type one followed by another meaning that I will display result from rd followed by result from cv followed by adz. But the actual method is very slow and it takes long time to retrieve back the results. what are the ways to improve the performance and will it matter using different data structure

    private List<AllJobModel> GetAllJobModelsOrder(List<AllJobModel> result)
    {
        var countItems = result.Count;
        List<AllJobModel> list = new List<AllJobModel>();
        while (countItems != 0)
        {
            for (int i = 0; i < countItems; i++)
            {
                if (result.ElementAt(i).JobImage.Contains("rd"))
                {
                    list.Add(result.ElementAt(i));
                    result.RemoveAt(i);
                    countItems--;
                    break;
                }
            }

            for (int i = 0; i < countItems; i++)
            {
                if (result.ElementAt(i).JobImage.Contains("cv"))
                {
                    list.Add(result.ElementAt(i));
                    result.RemoveAt(i);
                    countItems--;
                    break;
                }
            }
            for (int i = 0; i < countItems; i++)
            {
                if (result.ElementAt(i).JobImage.Contains("adz"))
                {
                    list.Add(result.ElementAt(i));
                    result.RemoveAt(i);
                    countItems--;
                    break;
                }
            }
            for(int i =0; i < countItems; i++)
            {
                if((!result.ElementAt(i).JobImage.StartsWith("rd") && !result.ElementAt(i).JobImage.StartsWith("adz")) && !result.ElementAt(i).JobImage.StartsWith("cv"))
                {
                    list.Add(result.ElementAt(i));
                    result.RemoveAt(i);
                    countItems--;
                    break;
                }
            }
        }    
       return list;
    }

Upvotes: 1

Views: 687

Answers (2)

thedutchguy
thedutchguy

Reputation: 11

Check out this link: https://cc.davelozinski.com/c-sharp/fastest-collection-for-string-lookups

Was very helpfull for me.

Regarding your specific problem. It looks like you're doing some filtering of the data. Linq has an easy way of doing that. I haven't test performance but if you can give me some example data ill try it for you. It could be something like this.

    private List<AllJobModel> GetAllJobModelsOrder(List<AllJobModel> result)
    {
        return result.Where(x => x.JobImage.Contains("rd") || x.JobImage.Contains("cv") || x.JobImage.Contains("adz")).ToList();
    }

Upvotes: 0

D Stanley
D Stanley

Reputation: 152491

This is a bad way to sort. You're effectively looping over the list 4 times, extracting specific groups of items each time. You also have a potential bug by removing items as you are iterating over the list. While there are many improvements you can make to your method, a better way would be to use OrderBy with the following sort condition:

list = result.OrderBy( m => m.JobImage.Contains("rd")  ? 1 : 
                            m.JobImage.Contains("cv")  ? 2 :
                            m.JobImage.Contains("adz") ? 3 : 
                            4)
             .ToList();

Upvotes: 2

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