How can I switch that code to use LINQ

Question

I know that is good practice use LINQ instead of iterative loops, can I modify this code to use LINQ?

List<string> priorsLstIDs = ServiceUtil.extractColumnValuesAsStringVals(tqrPriors,Helper.STUDY_ID);
List<DateTime> priorsLstDates = ServiceUtil.extractColumnValuesAsDateTimeVals(tqrPriors, "STUDY_DATE");
List<PriorElemSt> priorsElemLst = new List<PriorElemSt>(priorsLstIDs.Count);

PriorElemSt elem;

for (int i = 0; i < priorsLstIDs.Count; i++)
{
    elem = new PriorElemSt(priorsLstIDs[i], priorsLstDates[i]);
    priorsElemLst.Add(elem);
}

return filterStudyPriors(priorsElemLst);

Thanks.

Update: can the call to filterStudyPriors() method can be part of the LINQ?

Don't switch just because you read it's good practice. In tight loops, for example, iterative code can be much faster. — Roman Starkov, Sep 20 '11 at 14:01
I would add. I some cases iterative loops are much simpler for others to modify. Don't make everything a nail just because you have a hammer. — rerun, Sep 20 '11 at 14:03

abatishchev · Accepted Answer · 2011-09-20T15:09:34.677

8

IEnumerable<PriorElemSt> priorsElemLst = priorsLstIDs.Select((s,i) => new PriorElemSt(s, priorsLstDates[i]));
return filterStudyPriors(priorsElemLst);

edited Sep 20 '11 at 15:09

answered Sep 20 '11 at 14:00

abatishchev

98,240
88
296
433

The signature is IEnumerable – Delashmate Sep 20 '11 at 14:04
@Delashmate: Then the second part of my answer is more suitable for you. – abatishchev Sep 20 '11 at 14:05
This won't compile, in your answer `i` will be a string but needs to be an integer to pass to the list as an index. – Doctor Jones Sep 20 '11 at 14:05
@DoctaJonez: Now it will. Thanks. – abatishchev Sep 20 '11 at 14:10
You can make it shorter, since `s` already is `priorsLstIDs[i]` – Ray Sep 20 '11 at 14:50

Ray · Answer 2 · 2011-09-20T14:21:31.787

4

You can use the Zip method

var priorsElemLst = priorsLstIDs.Zip(
    priorsLstDates, (i, d) => new PriorElemSt(i, d))

In the above statement i is the item from priorsLstIds and d the item from priorsLstDates. They will be 'zipped' together using their positions in their lists.

edited Sep 20 '11 at 14:21

answered Sep 20 '11 at 14:02

Ray

45,695
27
126
169

score 4 · Answer 3 · answered Sep 20 '11 at 14:03

You could use the Enumerable.Range method like so:

//first get the range of indexes
var range = Enumerable.Range(0, priorsLstIDs.Count);
//now project a list of elements at each index
var priorsElemLst = range.Select(i => new PriorElemSt(priorsLstIDs[i], priorsLstDates[i])).ToList();

score 2 · Answer 4 · edited May 23 '17 at 09:59

it is not a best practice at all but only if you think it will improve the readability against a performance loss.

LINQ-to-Objects generally is going to add some marginal overheads (multiple iterators, etc). It still has to do the loops, and has delegate invokes, and will generally have to do some extra dereferencing to get at captured variables etc.

Is a LINQ statement faster than a 'foreach' loop?

How can I switch that code to use LINQ

4 Answers4