Concatenating List> takes a long time

Question

What I had tried till Now

string Value ="";
foreach (List<string> val in L1)
{
   Value = Value + string.Join(",", val) + " // ";
}

Where L1 is of datatype List <List<strings>>

This Works, But its take almost n half hour to complete Is there as many fastest and simple way to achieve this.

If you get a large amount of strings this uses a lot of memory and takes a lot of time to process, probably you should change your routine to streaming text and then performing some actions on it — Markiian Benovskyi, Aug 29 '17 at 09:56
When `L1` is a `List>`, this loop will throw an `InvalidCastException` because you declare `val` as `List`. — René Vogt, Aug 29 '17 at 09:57
After fixing ^, start using a `StringBuilder` to cut runtime in more than half. — Hatted Rooster, Aug 29 '17 at 09:58
I have Geojson Array whose coordinates value has this value List>>> — SimarjeetSingh Panghlia, Aug 29 '17 at 10:00
Is there any reason why you are getting data from GeoJSON as List>>>? Do you have a code snippet available for that? I feel that there may be something there you could improve upon to achieve desired results — Steven Brookes, Aug 29 '17 at 10:07

Gilad Green · Accepted Answer · 2017-08-29T09:59:55.983

I'd suggest use StringBuilder instead of concatenations in a loop like that:

StringBuilder builder = new StringBuilder();
foreach (List<string> val in L1)
{
    builder.Append(string.Join(",", val) + " // ");
}
string result = builder.ToString();

When concatenating in a loop it needs to copy the string everytime to a new position in memory with the extra allocated memory. StringBuilder prevents that.

You can also refer to:

@SimarjeetSinghPanghlia - you are welcome :) – Gilad Green Aug 29 '17 at 10:22 — Gilad Green, Aug 29 '17 at 10:22

Concatenating List> takes a long time

1 Answers1