Develop Reference

How to query DataTable

I have a datatable like that:
column1 column2 column3
a b c
d e f
I want to get index numbers of the cell "e" and i wrote these
int[] indexrowcol = new int[2];
for (int i = 0; i < dt.Columns.Count ; i++)
{
for (int j = 0; j < dt.Rows.Count; j++)
{
if (dt.Rows[i][j] == "e")
{
indexrowcol[0] = j; indexrowcol[1] = i;
}
}
}
How to write the same thing with usin LINQ? thanks.

I don't believe you have your original code implemented correctly to get what you're after. But at least it's more or less clear what you're trying to do. Here's some commented link code that can accomplish it.
var valToSearch = "e";
int[] indexrowcol = dt.AsEnumerable() // allows you to use linq
.SelectMany((row,rix) => // like 'Select', but stacks up listed output
row.ItemArray.Select( // ItemArray gets the row as an array
(col,cix) => new { rix, cix, value = col.ToString() }
)
)
.Where(obj => obj.value == valToSearch)
.Select(obj => new int[] { obj.rix, obj.cix })
.FirstOrDefault();
When I use the above code on the following DataTable, I get the result [1,1], which is the same result I get using your original code when I correct for the i/j reversal that existed at the time of this writing.
var dt = new DataTable();
dt.Columns.Add("Column1");
dt.Columns.Add("Column2");
dt.Columns.Add("Column3");
DataRow rw = dt.NewRow();
rw["Column1"] = "a";
rw["Column2"] = "b";
rw["Column3"] = "c";
dt.Rows.Add(rw);
rw = dt.NewRow();
rw["Column1"] = "d";
rw["Column2"] = "e";
rw["Column3"] = "f";
dt.Rows.Add(rw);
The reason your original code isn't quite right is that you use 'i' for columns and 'j' for rows, but then call dt.Rows[i][j], which is backwards. I highly recommend that your variables can be matched to what they are associated with. This is why I use names such as col, row, cix (column index), and rix to keep things straight.
In that vein, you might want to also output something other than an int[2]. Maybe a class or struct, or even just leave it as an anonymous object (get rid of the 'select' part of my query). Though I don't know your end use case, so I'll leave you alone on that.

How to add values in a validation list at once?

I'm trying to add values to a IExcelDataValidationList but the way I'm doing it right now is not very efficient.
I need to create many rows in my worksheet and populate a list for a certain cell for each of these rows. When I have many values to add to the list, this is taking forever.
for (var x = headerRowIndex + 1; x < 1000; x++)
{
var address = ExcelCellBase.TranslateFromR1C1($"R{x}C{colIndex}", 0, 0);
IExcelDataValidationList list = mainWorksheet.DataValidations.AddListValidation(address);
foreach (var e in values)
{
list.Formula.Values.Add(e);
}
}
You see how this can take a long time if values contain a lot of options.
Here's what I tried:
List<string> validationValues = new List<string>();
validationValues = values.ToList();
for (var x = headerRowIndex + 1; x < 1000; x++)
{
var address = ExcelCellBase.TranslateFromR1C1($"R{x}C{colIndex}", 0, 0);
var list = mainWorksheet.DataValidations.AddListValidation(address);
((List<string>)list.Formula.Values).AddRange(validationValues);
}
So I'm trying to add all values to the list at once. This compiles fine, but I'm getting this exception:
System.InvalidCastException: 'Unable to cast object of type
'DataValidationList' to type
'System.Collections.Generic.List`1[System.String]'.'
I've tried casting directly to DataValidationList but it's defined at private and only accessible by EPPlus itself.
Any ideas ?

Instead of creating IExcelDataValidationList per cell, create one for the whole column (address can include range of cells):
var address = ExcelCellBase.GetAddress(headerRowIndex + 1, colIndex, headerRowIndex + 1000, colIndex, true); // whole column
IExcelDataValidationList list = mainWorksheet.DataValidations.AddListValidation(address);
foreach (var e in values)
{
list.Formula.Values.Add(e);
}

Cassandra List Data Type C# get the last element

I have a List in Cassandra DB.
I use the following code to fetch them,
string query = "select name from table where userid = 'abcd' ;";
try
{
Connector connector = new Connector();
session = connector.Connect();
RowSet rows = session.Execute(query);
if (rows.Columns.Length > 0)
{
foreach (Row row in rows)
{
data = row["name"].ToString();
}
status = true;
}
}
else
{
// no rows
}
session.Cluster.Shutdown();
}
catch (Exception ex)
{
}
I need to convert this list object which is converting to string as of now to arrays so that I can fetch the last string as needed.
Is there any inbuilt method to do same?

I used the following code at last
foreach (Row row in rows)
{
object a = row["name"];
string[] arr = ((IEnumerable)a).Cast<object>()
.Select(x => x.ToString())
.ToArray();
int ab = arr.Length;
/*for all items*/
for(int i=0; i<ab;i++)
{
ltr.AppendText(arr[i]+","+i+" | ");
}
/*for only last item*/
string lastItem = arraystring[length - 1];
}
Combined many answers and did this and it works for me. let me know if there is any play with Enumerable method.

You can retrieve a Cassandra list<string> into a .NET List<T> using the Row.GetValue<T>() method:
var list = row.GetValue<List<string>>("name");
string lastValue = list[list.Count - 1];

How to Merge items within a List<> collection C#

I have a implememtation where i need to loop through a collection of documents and based on certain condition merge the documents .
The merge condition is very simple, if present document's doctype is same as later document's doctype, then copy all the pages from the later doctype and append it to the pages of present document's and remove the later document from the collection.
Note : Both response.documents and response.documents[].pages are List<> collections.
I was trying this but was getting following exception Once I remove the document.
collection was modified enumeration may not execute
Here is the code:
int docindex = 0;
foreach( var document in response.documents)
{
string presentDoctype = string.Empty;
string laterDoctype = string.Empty;
presentDoctype = response.documents[docindex].doctype;
laterDoctype = response.documents[docindex + 1].doctype;
if (laterDoctype == presentDoctype)
{
response.documents[docindex].pages.AddRange(response.documents[docindex + 1].pages);
response.documents.RemoveAt(docindex + 1);
}
docindex = docindex + 1;
}
Ex:
reponse.documents[0].doctype = "BankStatement" //page count = 1
reponse.documents[1].doctype = "BankStatement" //page count = 2
reponse.documents[2].doctype = "BankStatement" //page count = 2
reponse.documents[3].doctype = "BankStatement" //page count = 1
reponse.documents[4].doctype = "BankStatement" //page count = 4
Expected result:
response.documents[0].doctype = "BankStatement" //page count = 10
Please suggest.Appreciate your help.

I would recommend you to look at LINQ GroupBy and Distinct to process your response.documents
Example (as I cannot use your class, I give example using my own defined class):
Suppose you have DummyClass
public class DummyClass {
public int DummyInt;
public string DummyString;
public double DummyDouble;
public DummyClass() {
}
public DummyClass(int dummyInt, string dummyString, double dummyDouble) {
DummyInt = dummyInt;
DummyString = dummyString;
DummyDouble = dummyDouble;
}
}
Then doing GroupBy as shown,
DummyClass dc1 = new DummyClass(1, "This dummy", 2.0);
DummyClass dc2 = new DummyClass(2, "That dummy", 2.0);
DummyClass dc3 = new DummyClass(1, "These dummies", 2.0);
DummyClass dc4 = new DummyClass(2, "Those dummies", 2.0);
DummyClass dc5 = new DummyClass(3, "The dummies", 2.0);
List<DummyClass> dummyList = new List<DummyClass>() { dc1, dc2, dc3, dc4, dc5 };
var groupedDummy = dummyList.GroupBy(x => x.DummyInt).ToList();
Will create three groups, marked by DummyInt
Then to process the group you could do
for (int i = 0; i < groupedDummy.Count; ++i){
foreach (DummyClass dummy in groupedDummy[i]) { //this will process the (i-1)-th group
//do something on this group
//groupedDummy[0] will consists of "this" and "these", [1] "that" and "those", while [2] "the"
//Try it out!
}
}
In your case, you should create group based on doctype.
Once you create groups based on your doctype, everything else would be pretty "natural" for you to continue.
Another LINQ method which you might be interested in would be Distinct. But I think for this case, GroupBy would be the primary method you would like to use.

Use only "for loop" instead of "foreach".
foreach will hold the collection and cannot be modified while looping thru it.

Here is an example using groupBy, hope this help.
//mock a collection
ICollection<string> collection1 = new List<string>();
for (int i = 0; i < 10; i++)
{
collection1.Add("BankStatement");
}
for (int i = 0; i < 5; i++)
{
collection1.Add("BankStatement2");
}
for (int i = 0; i < 4; i++)
{
collection1.Add("BankStatement3");
}
//merge and get count
var result = collection1.GroupBy(c => c).Select(c => new { name = c.First(), count = c.Count().ToString() }).ToList();
foreach (var item in result)
{
Console.WriteLine(item.name + ": " + item.count);
}

Just use AddRange()
response.documents[0].pages.AddRange(response.documents[1].pages);
it will merge all pages of document[1] with the document[0] into document[0]

Comparing Sum Methods in C#

I am working on a section of a project that uses large number of sum methods. These sum methods are applied on a Datatable
To test the best method, I use the following
Datatable structure
class LogParser
{
public DataTable PGLStat_Table = new DataTable();
public LogParser()
{
PGLStat_Table.Columns.Add("type", typeof(string));
PGLStat_Table.Columns.Add("desc", typeof(string));
PGLStat_Table.Columns.Add("count", typeof(int));
PGLStat_Table.Columns.Add("duration", typeof(decimal));
PGLStat_Table.Columns.Add("cper", typeof(decimal));
PGLStat_Table.Columns.Add("dper", typeof(decimal));
PGLStat_Table.Columns.Add("occurancedata", typeof(string));
}
}
Following method is used to Fill the table
LogParser pglp = new LogParser();
Random r2 = new Random();
for (int i = 1; i < 1000000; i++)
{
int c2 = r2.Next(1, 1000);
pglp.PGLStat_Table.Rows.Add("Type" + i.ToString(), "desc" + i , c2, 0, 0, 0, " ");
}
Sum is applied on count column, where value of c2 is updated
Following Methods used to calculate Sum
Method 1 using Compute
Stopwatch s2 = new Stopwatch();
s2.Start();
object sumObject;
sumObject = pglp.PGLStat_Table.Compute("Sum(count)", " ");
s2.Stop();
long d1 = s2.ElapsedMilliseconds;
Method 2 using Foreach loop
s2.Restart();
int totalcount = 0;
foreach (DataRow dr in pglp.PGLStat_Table.Rows)
{
int c = Convert.ToInt32(dr["count"].ToString());
totalcount = totalcount + c;
}
s2.Stop();
long d2 = s2.ElapsedMilliseconds;
Method 3 using Linq
s2.Restart();
var sum = pglp.PGLStat_Table.AsEnumerable().Sum(x => x.Field<int>("count"));
MessageBox.Show(sum.ToString());
s2.Stop();
long d3 = s2.ElapsedMilliseconds;
After Comparison the results are
a) foreach is the fastest 481ms
b) next is linq 1016ms
c) and then Compute 2253ms
Query 1
I accidentally change "c2 to i" in the following statement
pglp.PGLStat_Table.Rows.Add("Type" + i.ToString(), "desc" + i , i, 0, 0, 0, " ");
The Linq statement produces an error
Arithmetic operation resulted in an overflow.
Whereas the Compute and Foreach loop are still able to complete the computation although maybe incorrect.
Is such a behaviour cause of concern or am I missing a directive ?
(also the figures computed are large)
Query 2
I was under the impression Linq does it fastest, is there a optimized method or parameter
that makes it perform better.
thanks for advice
arvind

Fastest sum is next (with precompute DataColumn and direct cast to int):
static int Sum(LogParser pglp)
{
var column = pglp.PGLStat_Table.Columns["count"];
int totalcount = 0;
foreach (DataRow dr in pglp.PGLStat_Table.Rows)
{
totalcount += (int)dr[column];
}
return totalcount;
}
Statistic:
00:00:00.1442297, for/each, by column, (int)
00:00:00.1595430, for/each, by column, Field<int>
00:00:00.6961964, for/each, by name, Convert.ToInt
00:00:00.1959104, linq, cast<DataRow>, by column, (int)
Other code:
static int Sum_ForEach_ByColumn_Field(LogParser pglp)
{
var column = pglp.PGLStat_Table.Columns["count"];
int totalcount = 0;
foreach (DataRow dr in pglp.PGLStat_Table.Rows)
{
totalcount += dr.Field<int>(column);
}
return totalcount;
}
static int Sum_ForEach_ByName_Convert(LogParser pglp)
{
int totalcount = 0;
foreach (DataRow dr in pglp.PGLStat_Table.Rows)
{
int c = Convert.ToInt32(dr["count"].ToString());
totalcount = totalcount + c;
}
return totalcount;
}
static int Sum_Linq(LogParser pglp)
{
var column = pglp.PGLStat_Table.Columns["count"];
return pglp.PGLStat_Table.Rows.Cast<DataRow>().Sum(row => (int)row[column]);
}
var data = GenerateData();
Sum(data);
Sum_Linq2(data);
var count = 3;
foreach (var info in new[]
{
new {Name = "for/each, by column, (int)", Method = (Func<LogParser, int>)Sum},
new {Name = "for/each, by column, Field<int>", Method = (Func<LogParser, int>)Sum_ForEach_ByColumn_Field},
new {Name = "for/each, by name, Convert.ToInt", Method = (Func<LogParser, int>)Sum_ForEach_ByName_Convert},
new {Name = "linq, cast<DataRow>, by column, (int)", Method = (Func<LogParser, int>)Sum_Linq},
})
{
var watch = new Stopwatch();
for (var i = 0; i < count; ++i)
{
watch.Start();
var sum = info.Method(data);
watch.Stop();
}
Console.WriteLine("{0}, {1}", TimeSpan.FromTicks(watch.Elapsed.Ticks / count), info.Name);
}

well you could improve a bit on the linq example (AsEnumerable) but this is expected behavior - Linq(2objects) cannot be faster as a loop (you could do even better by using a for(var i = ...) loop instead of the foreach) - I guess what you meant to do was using Linq2Sql - then the aggregation (sum) will be done on the database and it should be faster - but as you don't seem to use database-data...

Query 1.
As you can see in documentation Enumerable.Sum extension method throws an OverflowException on integer overflow. DataTable.Compute has no such a functionality as well as integer operations you use in Method 2.
UPDATE:
Query 2.
I was under the impression Linq does it fastest, is there a optimized method or parameter that makes it perform better.
AFAIK, there is no method's to optimize array summation algorithm (without using parallel computing). Linq doubles the time used by foreach. So, I don't think that's about linq performance but compute inefficiency (note that there is an overhead for query string interpretation).