LINQ: Add RowNumber Column

Question

How can the query below be modified to include a column for row number (ie: one-based index of results)?

var myResult = from currRow in someTable
               where currRow.someCategory == someCategoryValue
               orderby currRow.createdDate descending
               select currRow;

EDIT1: I'm looking for the results to be {idx, col1, col2...col-n} not {idx, row}.

EDIT2: The row number should correspond to result rows not the table rows.

EDIT3: I DataBind these results to a GridView. My goal was to add a row number column to the GridView. Perhaps a different approach would be better.

Answer 1

Use the method-syntax where Enumerable.Select has an overload with the index:

var myResult = someTable.Select((r, i) => new { Row = r, Index = i })
    .Where(x => x.Row.someCategory == someCategoryValue)
    .OrderByDescending(x => x.Row.createdDate);

Note that this approach presumes that you want the original index of the row in the table and not in the filtered result since i select the index before i filter with Where.

EDIT: I'm looking for the results to be {idx, col1, col2...col-n} not {idx, row}. The row number should correspond to result rows not the table rows.

Then select the anonymous type with all columns you need:

var myResult = someTable.Where(r => r.someCategory == someCategoryValue)
        .OrderByDescending(r => r.createdDate)
        .Select((r, i) => new { idx = i, col1 = r.col1, col2 = r.col2, ...col-n = r.ColN });

Answer 2

Use this Select method:

Projects each element of a sequence into a new form by incorporating the element's index.

Example:

var myResult = someTable.Where(currRow => currRow.someCategory == someCategoryValue)
                        .OrderByDescending(currRow => currRow.createdDate)
                        .Select((currRow, index) => new {Row = currRow, Index = index + 1});

---

In response to your edit:

If you want a DataTable as result, you can go the non-Linq way by simply using a DataView and add a additional column afterwards.

someTable.DefaultView.RowFilter = String.Format("someCategory = '{0}'", someCategoryValue);
someTable.DefaultView.Sort = "createdDate";
var resultTable = someTable.DefaultView.ToTable();
resultTable.Columns.Add("Number", typeof(int));
int i = 0;
foreach (DataRow row in resultTable.Rows)
    row["Number"] = ++i;

Answer 3

what about?

int i;
var myResult = from currRow in someTable
           where currRow.someCategory == someCategoryValue
           orderby currRow.createdDate descending
           select new {Record = i++, currRow};

Answer 4

Just for fun, here's an alternative to Select with two arguments:

var resultsWithIndexes = myResult.Zip(Enumerable.Range(1, int.MaxValue - 1),
                                      (o, i) => new { Index = i, Result = o });

Answer 5

According to you edit 1. NO, YOU CAN'T Linq returns the table as it is. You can build each column, but you lose the power of mapped entities.

This has been asked multiple times before: How do you add an index field to Linq results

Answer 6

There is no straightforward way if want to keep a flat list of columns (i.e. OP's Edit2) and also want a generic solution that works with any IEnumerable without requiring you to list out the set of expected columns.

However, there is a roundabout way to kinda go about it which is to dump the query results into a DataTable using the ToDataTable() method from here and then add a RowNumber column to that table.

var table = query.ToList().ToDataTable();
table.Columns.Add("RowNum", typeof(int));
int i = 0;
foreach (DataRow row in table.Rows)
    row["RowNum"] = ++i;

This would likely cause performance issues with large datasets but it's not insanely slow either. On my machine a dataset with ~6500 rows took 33ms to process.

If your original query returned an anonymous type, then that type definition will get lost in the conversion so you'll lose the static typing on the column names of the resulting IEnumerable when you call table.AsEnumerable(). In other words, instead of being able to write something like table.AsEnumerable().First().RowNum you instead have to write table.AsEnumerable().First()["RowNum"]

However, if you don't care about performance and really want your static typing back, then you can use JSON.NET to convert the DataTable to a json string and then back to a list based on the anonymous type from the original query result. This method requires a placeholder RowNum field to be present in the original query results.

var query  = (from currRow in someTable
            where currRow.someCategory == someCategoryValue
            orderby currRow.createdDate descending
            select new { currRow.someCategory, currRow.createdDate, RowNum = -1 }).ToList();
var table = query.ToDataTable();
//Placeholder RowNum column has to already exist in query results
//So not adding a new column, but merely populating it
int i = 0;
foreach (DataRow row in table.Rows)
    row["RowNum"] = ++i;
string json = JsonConvert.SerializeObject(table);
var staticallyTypedList = JsonConvert.DeserializeAnonymousType(json, query);
Console.WriteLine(staticallyTypedList.First().RowNum);

This added about 120ms to the processing time for my 6500 item dataset.

It's crazy, but it works.

Answer 7

I know I'm late to the party, but I wanted to show what worked for me.

I have a list of objects, and the object has an integer property on it for "row number"... or in this case, "Sequence Number". This is what I did to populate that field:

myListOfObjects = myListOfObjects.Select((o, i) => { o.SequenceNumber = i; return o; }).ToList();

I was surprised to see that this worked.

Answer 8

This one helped me in my case - Excel sheet extraction. anonymous type

var UploadItemList = ItemMaster.Worksheet().AsEnumerable().Select((x, index) => new
{
    Code = x["Code"].Value == null ? "" : x["Code"].Value.ToString().Trim(),
    Description = x["Description"].Value == null ? "" : x["Description"].Value.ToString().Trim(),
    Unit = x["Unit"].Value == null ? "" : x["Unit"].Value.ToString().Trim(),
    Quantity = x["Quantity"].Value == null ? "" : x["Quantity"].Value.ToString().Trim(),
    Rate = x["Rate"].Value == null ? "" : x["Rate"].Value.ToString().Trim(),
    Amount = x["Amount"].Value == null ? "" : x["Amount"].Value.ToString().Trim(),
    RowNumber = index+1
}).ToList();

Answer 9

int Lc = 1;

var Lst = LstItemGrid.GroupBy(item => item.CategoryName)
    .Select(group => new { CategoryName = group.Key, Items = group.ToList() ,RowIndex= Lc++ })
    .ToList();