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How to use CopyToDataTable() method in LINQ successfully using below example only?

I have been trying something with LINQ to get all the data from a table customers in a data table. I have used SQL to LINQ class here.
SampleDataContext sdc = new SampleDataContext();
DataTable Cust = new DataTable();
// var query = from c in sdc.customers
// select c;
var query = (IEnumerable<DataRow>)sdc.customers.Select(c => c);
Cust = query.CopyToDataTable();
Console.WriteLine(Cust);
Now when I run this, I get an exception:
Unable to cast object of type 'System.Data.Linq.DataQuery1[BasicLearning.customer]' to type 'System.Collections.Generic.IEnumerable1[System.Data.DataRow]'
Why am I getting this exception?
ANS - from my understanding, which may be wrong, the (IEnumerable<DataRow>) casting in above logic won't work because the result set is not an IEnumerable but IQueryable. But I am not sure if I understand this exception correctly.
So, here I am stuck now, on how to get this code running. I want to use CopyToDataTable() method. But Casting is not working.
It would be great if anyone could help me understand what I am doing wrong here and how to correct it.

as #Svyatoslav Danyliv mention you need to convert object to table. there is an extention which dynamically convert object to datatable.
void Main()
{
DataTable Cust = new DataTable();
//var query = from c in sdc.customers
// select c;
var query = Customers.Select(c => c).ConvertClassToDataTable<Customer>().AsEnumerable();
Cust = query.CopyToDataTable();
Console.WriteLine(Cust);
}
public static class Extensions
{
public static DataTable ConvertClassToDataTable<T>(this IEnumerable<T> list)
{
Type type = typeof(T);
var properties = type.GetProperties();
DataTable dataTable = new DataTable();
foreach (PropertyInfo info in properties)
{
dataTable.Columns.Add(new DataColumn(info.Name, Nullable.GetUnderlyingType(info.PropertyType) ?? info.PropertyType));
}
foreach (T entity in list)
{
object[] values = new object[properties.Length];
for (int i = 0; i < properties.Length; i++)
{
values[i] = properties[i].GetValue(entity);
}
dataTable.Rows.Add(values);
}
return dataTable;
}
}

How to melt a DataTable in C# .NET (wide to long format)?

How to melt a DataTable in C# (wide to long format) as Python Pandas.melt does? https://pandas.pydata.org/docs/reference/api/pandas.melt.html
Is there any method already implemented? If not, how the code for melting a DataTable would
For example:
I have one DataTable which is in wide format, that is that has one row per id and has as many columns as variables. I would like to transform this DataTable to long format that has as many rows as combinations of id with each variable column. You can see this example in top image.
Please, if there is not clear enough visit Pandas documentation, there is more clear. (https://pandas.pydata.org/docs/reference/api/pandas.melt.html)
Note: I would like a solution that is DataTable independent, that is, that the solution is able to take parameters as id_vars, value_vars, etc... like Pandas.melt does
Any help is appreciated.

I don't know that Melt method but according to docs it seems to be an unpivot method:
public static DataTable MeltTable(DataTable inputTable, string outputColumn, params string[] unpivotColumns)
{
DataTable resultTable = new DataTable();
DataColumn col = new DataColumn(outputColumn, inputTable.Columns[outputColumn].DataType);
resultTable.Columns.Add(col);
resultTable.Columns.Add("Variable");
resultTable.Columns.Add("Value");
foreach(string unpivotColumn in unpivotColumns)
{
foreach (DataRow row in inputTable.Rows)
{
resultTable.Rows.Add(row[outputColumn], unpivotColumn, row[unpivotColumn]);
}
}
return resultTable;
}
You use it in this way:
DataTable table = new DataTable();
table.Columns.Add("Name");
table.Columns.Add("Course");
table.Columns.Add("Age", typeof(int));
table.Rows.Add("Tim", "Masters", 47);
table.Rows.Add("Bob", "Graduate", 19);
table.Rows.Add("Sheila", "Graduate", 20);
DataTable resultTable = MeltTable(table, "Name", "Course", "Age");
Result:
Name Variable Value
Tim Course Masters
Bob Course Graduate
Sheila Course Graduate
Tim Age 47
Bob Age 19
Sheila Age 20

#TimSchmelter gave me the answer but I modified a little bit to be a more general solution. Here's the code:
public static List<string> GetDifferenceColumns(DataTable dt, List<string> diffCols)
{
string[] columns = GetColumnsList(dt).ToArray();
IEnumerable<string> differenceColumns = from column in columns.Except(diffCols.ToArray()) select column;
return differenceColumns.ToList();
}
public static DataTable Melt(DataTable dt, List<string> idCols = null, List<string> varCols = null)
{
string errorPrefixString = "Error in DataProcessing Melt Method:\n";
bool varsColsIsNull = (varCols == null || varCols.Count == 0);
bool idColsIsNull = (idCols == null || idCols.Count == 0);
string varsName = "Variable";
string valueName = "Value";
if (dt.Rows.Count == 0)
{
throw new Exception(errorPrefixString + "DataTable is empty");
}
if (varsColsIsNull && varsColsIsNull)
{
throw new Exception(errorPrefixString+"You should past at least varCols or idCols");
}
if (varsColsIsNull)
{
varCols = GetDifferenceColumns(dt, idCols);
}
if (idColsIsNull)
{
idCols = GetDifferenceColumns(dt, varCols);
}
DataTable resultTable = new DataTable();
// Creating final columns of resultTable
foreach (string id in idCols)
{
resultTable.Columns.Add(id);
}
resultTable.Columns.Add(varsName);
resultTable.Columns.Add(valueName);
// Populating resultTable with the new rows
// generated by unpivoting varCols
foreach (string varCol in varCols)
{
foreach (DataRow row in dt.Rows)
{
DataRow resultRow = resultTable.NewRow();
foreach(string id in idCols)
{
resultRow[id] = row[id]; // create id cols
}
resultRow[varsName] = varCol;
resultRow[valueName] = row[varCol];
resultTable.Rows.Add(resultRow);
}
}
return resultTable;
}
How to use it:
DataTable dt = new DataTable();
dt.Columns.Add("Name");
dt.Columns.Add("Course");
dt.Columns.Add("Age");
dt.Rows.Add("Tim", "Masters", 47);
dt.Rows.Add("Bob", "Graduate", 19);
dt.Rows.Add("Sheila", "Graduate", 20);
List<string> varCols = new List<string> { "Course", "Age" };
DataTable finalDataTable = Melt(dt, varCols: varCols);

Convert DataTable to LINQ Anonymous Type

I want a function which takes in a datatable & returns a List (object is not DataRow)
Eg. :
I know I can do this (but this requires column names to be known) :
// Datatable dt = Filled from a Database query & has 3 columns Code,Description & ShortCode
List<object> rtn = new List<object>();
var x = from vals in dt.Select()
select new
{
Code = vals["Code"],
Description = vals["Description"],
ShortCode = vals["ShortCode"],
};
rtn.AddRange(x)
return rtn;
What i want is a generic version so that i can pass in any datatable & it will generate based on column names in the datatable.

Since the property names are not known at compile time and you want to use the data for JSON serialization, you can use the following to create a list of dictionary. If you use Newtonsoft JSON, then the serialization takes care of converting the key value pairs in a JSON object format.
IEnumerable<Dictionary<string,object>> result = dt.Select().Select(x => x.ItemArray.Select((a, i) => new { Name = dt.Columns[i].ColumnName, Value = a })
.ToDictionary(a => a.Name, a => a.Value));

In order to dynamically create properties so as to treat different dataTables with different set of Columns, we can use the System.Dynamic.ExpandoObject. It basically implements, IDictionary <string,object>. The format, which can easily be converted to JSON.
int colCount = dt.Columns.Count;
foreach (DataRow dr in dt.Rows)
{
dynamic objExpando = new System.Dynamic.ExpandoObject();
var obj = objExpando as IDictionary<string, object>;
for (int i = 0; i < colCount; i++)
{
string key = dr.Table.Columns[i].ColumnName.ToString();
string val = dr[key].ToString();
obj[key] = val;
}
rtn.Add(obj);
}
String json = new System.Web.Script.Serialization.JavaScriptSerializer().Serialize(rtn);

You can use the following generic function:-
private static List<T> ConvertDataTable<T>(DataTable dt)
{
List<T> data = newList<T>();
foreach (DataRowrow in dt.Rows)
{
Titem = GetItem<T>(row);
data.Add(item);
}
return data;
}
private static TGetItem<T>(DataRow dr)
{
Type temp = typeof(T);
T obj =Activator.CreateInstance<T>();
foreach (DataColumncolumn in dr.Table.Columns)
{
foreach (PropertyInfopro in temp.GetProperties())
{
if (pro.Name == column.ColumnName)
pro.SetValue(obj,dr[column.ColumnName], null);
else
continue;
}
}
return obj;
}
Please check my article, which has complete demonstration on how to use this generic method.

Here is the original question:
// Datatable dt = Filled from a Database query & has 3 columns Code,Description & ShortCode
List<object> rtn = new List<object>();
var x = from vals in dt.Select()
select new
{
Code = vals["Code"],
Description = vals["Description"],
ShortCode = vals["ShortCode"],
};
rtn.AddRange(x)
return rtn;
Just replace with
List<object> rtn = JsonConvert.DeserializeObject<List<object>>(JsonConvert.SerializeObject(dt));

You will have the provide the anonymous object as a parameter and use json/xml serialization:
protected static List<T> ToAnonymousCollection<T>(DataTable dt, T anonymousObject)
{
List<DataColumn> dataColumns = dt.Columns.OfType<DataColumn>().ToList();
return dt.Rows.OfType<DataRow>().Select(dr =>
{
Dictionary<string, object> dict = new Dictionary<string, object>();
dataColumns.Each(dc => dict.Add(dc.ColumnName, dr[dc]));
return JsonConvert.DeserializeAnonymousType(JsonConvert.SerializeObject(dict), anonymousObject);
}).ToList();
}
Usage:
var anonymousCollection = ToAnonymousCollection(dt, new { Code = [ColumnTypeValue, eg. 0], Description = [ColumnTypeValue, eg. string.Empty], ShortCode = Code=[ColumnTypeValue, eg. 0] })

epplus using LoadFromCollection with anonymous types

I have a IEnumerable<object> dataSource which contains a collection anonymous types. The actual structure of the anonymous type won't be known at design time, so I'm trying to find a generic solution that can handle any anonymous type.
How can I load them into epplus to create a spreadsheet? I have a worksheet called ws and I tried:
ws.Cells["A1"].LoadFromCollection(dataSource, true);
However when that runs it outputs all of the anonymous type's properties into a single cell:
{ Id = 10000, Title = This is a test }
I've tried passing in MemberInfo using:
var members = dataSource.First().GetType().GetMembers();
ws.Cells["A1"].LoadFromCollection(this._dataSource, true,
TableStyles.Medium1, BindingFlags.Public, members);
But that throws an exception:
Supplied properties in parameter Properties must be of the same type as T
Any suggestions on how I can create a spreadsheet using anonymous types in c#?

I have tested
using (var excel = new OfficeOpenXml.ExcelPackage())
{
var sheet = excel.Workbook.Worksheets.Add("Test");
sheet.Cells["A1"].LoadFromCollection(dataSource, true);
excel.SaveAs(new FileInfo(#"C:\Temp\Test.xlsx"));
}
with this sample data:
var dataSource = Enumerable.Range(1, 100).Select(i => new{ ID=i, Title="Title " + i });
It works fine. It creates two columns with the correct headers and 100 rows.
But you should use anonymous types only if you know the structure at compile time.
You could use a DataTable and LoadFromDataTable instead. Since i don't know how you create the anonymous type i show you just a small sample:
DataTable dataSource = new DataTable();
dataSource.Columns.Add("Id"); // default type is string
dataSource.Columns.Add("Title");
// add other columns
dataSource.Rows.Add("1", "Title1");
// add other rows
using (var excel = new OfficeOpenXml.ExcelPackage())
{
var sheet = excel.Workbook.Worksheets.Add("Test");
sheet.Cells["A1"].LoadFromDataTable(dataSource, true);
excel.SaveAs(new FileInfo(#"C:\Temp\Test.xlsx"));
}

You could group the anonymous types to make it easier for exporting with dataTables. The bug "Supplied properties in parameter Properties must be of the same type as T" is still there and a workaround is using DataTables.
// Imagine list is your main datasource
IEnumerable<object> list = Enumerable.Empty<object>(); // Data Source of <object>
// Added anon types at runtime added to the object list
var anonTypesOne = new object[]
{
new { GuidID = Guid.NewGuid(), StringProperty = "the string property" },
new { IntegerID = 1, IntegerProperty = 99 }
};
var anonTypesTwo = new object[]
{
new { StringID = "1", BooleanProperty = true, NumberProperty = 3, StringProperty = "Four" },
new { GuidID = Guid.NewGuid(), NumberThree = 3 },
new { GuidID = Guid.NewGuid(), NumberThree = 3 },
new { GuidID = Guid.NewGuid(), NumberThree = 3 }
};
list = list.Concat(anonTypesOne).Concat(anonTypesTwo);
// Grouping works on anon types so we can group the export into their own tables
var groupings = list.GroupBy(i => i.GetType());
using(var package = new ExcelPackage(new FileInfo("C:\\Temp\\Anon.xlsx")))
{
var ws = package.Workbook.Worksheets.Add("Anonymous Types");
// add each "anon type matched grouping"
foreach(var grouping in groupings)
{
var isNew = ws.Dimension == null; // the sheet is empty if Dimension is null.
var row = 0;
if(isNew)
{
row = 1; // start from the first row
}
else
{
// otherwise there are tables already, start from the bottom
row = ws.Dimension.End.Row;
}
// because of EPP inheritance bug of T, we can just use dataTable
DataTable dt = new DataTable(grouping.Key.Name);
var properties = grouping.Key.GetProperties(); // Get anon type Properties
foreach(var property in properties)
{
dt.Columns.Add(property.Name);
}
foreach(var item in grouping.ToList())
{
var dataRow = dt.NewRow();
foreach(var p in properties) // populate a single row
{
dataRow[p.Name] = p.GetValue(item); // item is anon object instance
}
dt.Rows.Add(dataRow);
}
if(isNew) // load into the top most left cell of the worksheet
ws.Cells[1, 1].LoadFromDataTable(dt, PrintHeaders: true);
else // load from the dimension of current items + 1 row for spacing
ws.Cells[ws.Dimension.End.Row + 1, 1].LoadFromDataTable(dt, PrintHeaders: true);
ws.InsertRow(ws.Dimension.End.Row + 2, 5); // Insert some padding between each group
}
package.Save();
}

I was, this thread is older, but I'm looking for the same problem.
With the following code (VB) I have success.
Carsten
Dim targetFile = New IO.FileInfo(sFN)
Dim dataSource = Enumerable.Range(0, 1).Select(Function(i) New With {.ID = 1000, .Titel = "This is a test "}).ToList
Using epp = New OfficeOpenXml.ExcelPackage(targetFile)
Dim ws = epp.Workbook.Worksheets.Add("lst_Anonymous")
ws.Cells(1, 1).LoadFromCollection(dataSource, True,
OfficeOpenXml.Table.TableStyles.Medium1,
Reflection.BindingFlags.Public,
dataSource.GetType.GetGenericArguments()(0).GetProperties)
epp.Save()
End Using

extracting contents of Datatable into list C#

I am experimenting to take datatable contents into a list. I am using following code but its not working correctly.
public List<object> ShowMessage()
{
List<object> obj = new List<object>();
DataTable dt = new DataTable();
dt.Columns.Add("ID");
dt.Columns.Add("Name");
dt.Rows.Add("1","AAA");
dt.Rows.Add("2", "BBB");
dt.Rows.Add("3", "CCC");
foreach (DataRow dr in dt.Rows)
{
obj.Add(dr);
}
return obj;
}
I am new and not sure I am doing in a right way or I need to use some thing else. Any suggestion will be highly appreciated.
Thanks.

Converting your DataTable to list of name strings (with help of Linq to DataSet):
List<string> names =
dt.AsEnumerable().Select(r => r.Field<string>("Name")).ToList();
Which is same as
List<string> names = new List<string>();
foreach(DataRow r in dt.Rows)
names.Add((string)r["Name"]);

I think you are making a too abstract example. This one use a possible class named Person
public class Person
{
public int PersonID;
public string Name;
// other fields will follow in future
}
public List<Person> GetPersonList()
{
List<Person> people = new List<Person>();
// This is just as example, because in real code
// you get this table from a database
DataTable dt = new DataTable();
dt.Columns.Add("ID");
dt.Columns.Add("Name");
dt.Rows.Add(1,"John");
dt.Rows.Add(2, "Mark");
dt.Rows.Add(3, "Steve");
// Loop over the rows and construct a Person instance for every row
// Add that row to the List<Person> to return
foreach (DataRow dr in dt.Rows)
{
Person p = new Person() {PersonID =Convert.ToInt32(dr[0]), Name = dr[1].ToString());
people.Add(p);
}
return people;
}
By the way, this pattern of code, is exactly what a good ORM do for you. A little research for Entity Framework or Dapper would be very useful

#Karni: you were close to what you need. however below is the modified version of your code example so that you achieve what you need..
public class Obj
{
public int ID { get; set; }
public string Name { get; set; }
}
public class ListObj : List<Obj>
{
}
class Program
{
static void Main(string[] args)
{
DataTable dt = new DataTable();
dt.Columns.Add("ID");
dt.Columns.Add("Name");
dt.Rows.Add("1", "AAA");
dt.Rows.Add("2", "BBB");
dt.Rows.Add("3", "CCC");
ListObj objListObj = new ListObj();
//to fill the list / collection
for (int i = 0; i < dt.Rows.Count; i++)
{
objListObj.Add(new Obj() { ID = Convert.ToInt16(dt.Rows[i][0]), Name = dt.Rows[i][1].ToString() });
}
//To verify if the collection is filled.
foreach (var item in objListObj)
{
Console.WriteLine(item.ID + " : " + item.Name);
}
Console.Read();
}
}