How would I convert only a subset of column values from a DataRow into a string array using LINQ?

Question

EDIT: I'm giving the credit to Nick as his answer pointed me in the right direction. In his answer he had set all DataColumns to be retrieved as String, but not all columns in the DataTable were strings. Also Select() was appropriate to get individual rows whereas SelectMany() joined all column values for multiple rows into a single array, or one big row if you will. Here is the solution:

using (dataTable)
using (var sw = new StreamWriter(resultPath, false))
{
    DataColumn[]
          exclCols = { dataTable.Columns["registryvalue"] }, //excluded
          inclCols = dataTable.Columns //included columns
                              .Cast<DataColumn>()
                              .Except(exclCols)
                              .ToArray();

    sw.WriteLine(String.Join( //header line
                 ",", inclCols.Select(column => column.ColumnName).ToArray()));

    foreach (var row in dataTable.AsEnumerable().Select(
            dataRow => inclCols.Select(column => dataRow.Field<Object>(column))))
    {
        sw.WriteLine(String.Join(
                     ",", row.Select(r => (r == null) ? 
                     "" : r.ToString()).ToArray()));
    }
}

I'm using foreach to loop through the rows of a DataTable. There are only certain columns' values that I want from the DataRow and I want to convert this subset of values into a string array (we'll call it myStringArray). The end result is:

StreamWriter.WriteLine(String.Join(",", myStringArray))

I can accomplish writing the line without using LINQ, but then that doesn't help me better understand LINQ. Getting the subset of column names I want into an array is easy, but I just don't know how to use that array to get only those columns' data from the DataRow.

I re-read your question after posting my answer below... Do you need just one column's data or do you need to combine strings from multiple columns? — Nick Strupat
– Nick Strupat, Commented Feb 15, 2012 at 23:58
Yeah but I think you will end up with an Array of String[]. Because you are going to get a String[] for each row in your DataTable. Maybe you should clarify this in your question. — Orkun
– Orkun, Commented Feb 16, 2012 at 0:00
I'm looking to get a subset of all the objects that make up a DataRow and then convert those objects into a single string array. — user1197862
– user1197862, Commented Feb 16, 2012 at 14:07

Nick Strupat · Accepted Answer · 2012-02-16 04:29:55Z

2

EDIT 2:

Here's how to do it with LINQ

var columnNames = new [] { "Column1", "Column2", "Column3" };
var strings = dataTable.AsEnumerable().SelectMany(dataRow => columnNames.Select(columnName => dataRow.Field<String>(columnName)));

EDIT:

I'm not sure how to do that with LINQ. It is simple to express using two foreach loops though

String [] columnNames = new String [] { "Column1", "Column2", "Column3" };
var myStrings = new List<String>();
foreach (DataRow dataRow in dataTable.Rows)
    foreach (String columnName in columnNames)
        myStrings.Add(dataRow.Field<String>(columnName));

ORIGINAL:

You'll need DataTable.AsEnumerable() extension method to use LINQ against your DataTable

Something like this will do the job...

var myStrings = from dataRow in dataTable.AsEnumerable()
                select dataRow.Field<String>("TheColumnName");

edited Feb 16, 2012 at 4:29

answered Feb 15, 2012 at 23:56

Nick Strupat

5,0925 gold badges47 silver badges58 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user1197862 Over a year ago

I was hoping to avoid explicitly naming the columns I wanted, but rather use the array that contains the column names I want included.

user1197862 Over a year ago

Your Edit2 got me going in the right direction. See my edit to the original post. Thanks!

Prof Von Lemongargle · Accepted Answer · 2012-02-16 00:00:42Z

0

There are probably a variety of answers to this, but I will take a stab at one that might be illuminating. My syntax is rusty, so please forgive errors, the theory should be good.

foreach (var row in from it in myDataTable select new { Col1 = it.Col1, Col2 = it.Col2 })
    //Do something with the subset of rows that is interesting.

This will get you an anonymous type that has the fields Col1 and Col2 in it. You can select any subset you like.

foreach (var myArray in from it in myDataTable select new string[] { it.Col1, it.Col2 })
    //Do something with the string array

I have not tried this as a string array has never been a target, but it you experiment you can probably make it work.

LINQ offers a variety of syntax choices, this one assumes you are in c# using declarative syntax.

answered Feb 16, 2012 at 0:00

Prof Von Lemongargle

3,77833 silver badges31 bronze badges

1 Comment

user1197862 Over a year ago

Unfortunately this returns only an array of basically the same information I already have in my included columns array.

Collectives™ on Stack Overflow

How would I convert only a subset of column values from a DataRow into a string array using LINQ?

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related