I am looping through a array of datarows and when a particular random item is not valid I want to remove that item and get the new total to get another random item.
But when I delete a datarow the datarow does not go away... And yes there is probably a much better way to do this but I am not smart enough to do it..
Instead of removing the row I see this inside
ItemArray = podLps[1].ItemArray threw an exception of type System.Data.RowNotInTableException
//PHASE 1: Get all LPs in the pod and add to collection
List<DataRow> allLps = dtLp.AsEnumerable().ToList();
DataRow[] podLps = allLps.Where(x => x.ItemArray[0].ToString() == loPod).ToArray();
//PHASE 2: Pick a random LP from collection that has valid WAVE1
for (int i = podLps.Count(); i > 0; i--)
{
//Recount items in collection since one may have been removed
int randomIndex = random.Next(podLps.Count());
var randomLpUserId = podLps[randomIndex].ItemArray[1].ToString();
var randomLpWave1 = int.Parse(podLps[randomIndex].ItemArray[2].ToString());
//Get WAVE1 # for selected LP
lpNumberOfLoans = GetNumberOfLoans(session, randomLpUserId);
//check if LP has valid WAVE1 then use this person
if (randomLpWave1 > lpNumberOfLoans)
{
return randomLpUserId;
}
else
{
podLps[randomIndex].Delete();
}
}
look at this example and it should point you in the right direction for removing rows I just tested it and it works
for (int i = myDataTable.Rows.Count - 1; i >= 0; i--)
{
DataRow row = myDataTable.Rows[i]; //Remove
if (myDataTable.Rows[i][0].ToString() == string.Empty)
{
myDataTable.Rows.Remove(row);
}
}
I would suggest to use a List for podLps instead of an array.
Then you can use .RemoveAt as Jaco mentioned (dosn't work for arrays).
DataRow.Delete() just flags the Row to be deleted in the next update of your DataTable.
The easiest method is to convert your array of DataRow[] to a List, call RemoveAt and then convert the list back to an array:
var dest = new List<>(podLps);
dest.RemoveAt(randomIndex);
podLps = dest.ToArray();
Related
I have the following method that returns a trimmed down copy of a datatable based on the user selecting which 6 columns to keep. My problem is the datatable can be quite large and is taking up quite a bit of memory. By creating the initial copy, this is causing the system to have to start writing to the page file and slowing the application down considerably.
I'm wondering if it is possible to create a datatable copy but of only the specified columns (can be identified through name or index, doesn't matter) rather than creating the copy then removing the unnecessary columns?
This question appears to be asking the same thing but in VB.net.
private DataTable CreateCleanData()
{
var cleanedDataTable = _loadedDataData.Copy();
var columnsToKeep = new List<string>();
columnsToKeep.Add(1.SelectedValue.ToString());
columnsToKeep.Add(2.SelectedValue.ToString());
columnsToKeep.Add(3.SelectedValue.ToString());
columnsToKeep.Add(4.SelectedValue.ToString());
columnsToKeep.Add(5.SelectedValue.ToString());
columnsToKeep.Add(6.SelectedValue.ToString());
for (var i = cleanedDataTable.Columns.Count - 1; i >= 0; i--)
if (!columnsToKeep.Contains(cleanedDataTable.Columns[i].ColumnName))
cleanedDataTable.Columns.Remove(cleanedDataTable.Columns[i]);
cleanedDatTable.AcceptChanges();
GC.Collect();
return cleanedDataTable;
}
You could use this method, basically just use Clone instead of Copy:
public static DataTable CreateCleanData(DataTable source, params int[] keepColumns)
{
var cleanedDataTable = source.Clone(); // empty table but same columns
for (int i = cleanedDataTable.Columns.Count - 1; i >= 0; i--)
{
if (!keepColumns.Contains(i))
cleanedDataTable.Columns.RemoveAt(i);
}
cleanedDataTable.BeginLoadData();
foreach (DataRow sourceRow in source.Rows)
{
DataRow newRow = cleanedDataTable.Rows.Add();
foreach (DataColumn c in cleanedDataTable.Columns)
{
newRow.SetField(c, sourceRow[c.ColumnName]);
}
}
cleanedDataTable.EndLoadData();
return cleanedDataTable;
}
I'm back to haunt your dreams! I'm working on comparing some values in a complex loop. List 1 is a list of questions/answers, List 2 is also a list of questions/answers. I want to compare List 1 to List 2 and have duplicates removed from List 1 before merging it with List 2. My problem is in the current seed data I have the two items in List 1 match against List 2, but only one is removed instead of both.
I've been at this a couple days and my head is ready to explode, so I hope I can find some help!
Here's code for you:
//Fetching questions/answers which do not have an attempt
//Get questions, which automatically pull associated answers thanks to the model
List<QuizQuestions> notTriedQuestions = await db.QuizQuestions.Where(x=>x.QuizID == report.QuizHeader.QuizID).ToListAsync();
//Compare to existing attempt data and remove duplicate questions
int i = 0;
while(i < notTriedQuestions.Count)
{
var originalAnswersCount = notTriedQuestions.ElementAt(i).QuizAnswers.Count;
int j = 0;
while(j < originalAnswersCount)
{
var comparedID = notTriedQuestions.ElementAt(i).QuizAnswers.ElementAt(j).AnswerID;
if (report.QuizHeader.QuizQuestions.Any(item => item.QuizAnswers.Any(x => x.AnswerID == comparedID)))
{
notTriedQuestions.RemoveAt(i);
//Trip while value and cause break out of loop, otherwise you result in a catch
j = originalAnswersCount;
}
else
{
j++;
}
}
i++;
}
//Add filtered list to master list
foreach (var item in notTriedQuestions)
{
report.QuizQuestions.Add(item);
}
Try List.Union It is meant for exactly this sort of thing.
I'm after some help with how to query a list and return back the index, but not using Linq. I've seen many example where Linq is used, but the software I'm writing the query into doesn't support Linq. :(
So example to get us going:
List<string> location = new List<string>();
location.add(#"C:\test\numbers\FileName_IgnoreThis_1.jpg");
location.add(#"C:\test\numbers\FileName_IgnoreThis_2.jpg");
location.add(#"C:\test\numbers\FileName_ImAfterThis_3.jpg");
location.add(#"C:\test\numbers\FileName_IgnoreThis_4.jpg");
location.add(#"C:\test\numbers\FileName_ImAfterThis_5.jpg");
So this list will be populated with probably a few hundred records, what I need to do is query the list for the text "ImAfterThis" then return the index number location for this item into a string array but without using Linq.
The desired result would be 2 and 4 being added to the string array.
I was thinking of doing a for loop through the list, but is there a better way to achieve this?
List<int> results = new List<int>();
int i = 0;
foreach (string value in location)
{
if (value.Contains("IAfterThis"))
{
results.Add(i);
Console.WriteLine("Found in Index: " + i);
}
i++;
}
Console.ReadLine();
Thanks in advance.
If you want to get just the first occurrence you could simply use the IndexOf() method.
If you want all occurrences of string "whatever" then a for loop would certainly work for you. For the sake of argument here I've capture the indexes in another list:
string MyString = "whatever";
List<int> indexes = new List();
for (int i = 0; i < location.Count; i++)
{
if (location[i] == MyString)
{
indexes.Add(i);
}
}
I want to find all rows in a DataTable where each of a group of columns is a duplicate. My current idea is to get a list of indexes of all rows that appear more than once as follows:
public List<int> findDuplicates_New()
{
string[] duplicateCheckFields = { "Name", "City" };
List<int> duplicates = new List<int>();
List<string> rowStrs = new List<string>();
string rowStr;
//convert each datarow to a delimited string and add it to list rowStrs
foreach (DataRow dr in submissionsList.Rows)
{
rowStr = string.Empty;
foreach (DataColumn dc in submissionsList.Columns)
{
//only use the duplicateCheckFields in the string
if (duplicateCheckFields.Contains(dc.ColumnName))
{
rowStr += dr[dc].ToString() + "|";
}
}
rowStrs.Add(rowStr);
}
//count how many of each row string are in the list
//add the string's index (which will match the row's index)
//to the duplicates list if more than 1
for (int c = 0; c < rowStrs.Count; c++)
{
if (rowStrs.Count(str => str == rowStrs[c]) > 1)
{
duplicates.Add(c);
}
}
return duplicates;
}
However, this isn't very efficient: it's O(n^2) to go through the list of strings and get the count of each string. I looked at this solution but couldn't figure out how to use it with more than 1 field. I'm looking for a less expensive way to handle this problem.
Try this:
How can I check for an exact match in a table where each row has 70+ columns?
The essence is to make a set where you store hashes for rows and only do comparisons between rows with colliding hashes, complexity will be O(n)
...
If you have a large number of rows and storing the hashes themselves is an issue (an unlikely case, but still...) you can use a Bloom filter. The core idea of a Bloom filter is to calculate several different hashes of each row and use them as an address in a bitmap. As you're scanning through the rows you can double-check the rows that already have all the bits in the bitmap previously set.
I get the following error while I try to delete a row while looping through it.
C#: Collection was modified; enumeration operation may not execute
I've been doing some research for a while, and I've read some similar posts here, but I still haven't found the right answer.
foreach (DataTable table in JobsDS.Tables)
{
foreach (DataRow row in table.Rows)
{
if (row["IP"].ToString() != null && row["IP"].ToString() != "cancelled")
{
string newWebServiceUrl = "http://" + row["IP"].ToString() + "/mp/Service.asmx";
webService.Url = newWebServiceUrl;
string polledMessage = webService.mpMethod(row["IP"].ToString(), row["ID"].ToString());
if (polledMessage != null)
{
if (polledMessage == "stored")
{
removeJob(id);
}
}
}
}
}
any help would be greatly appreciated
Instead of using foreach, use a reverse for loop:
for(int i = table.Rows.Count - 1; i >= 0; i--)
{
DataRow row = table.Rows[i];
//do your stuff
}
Removing the row indeed modifies the original collection of rows. Most enumerators are designed to explode if they detect the source sequence has changed in the middle of an enumeration - rather than try to handle all the weird possibilities of foreaching across something that is changing and probably introduce very subtle bugs, it is safer to simply disallow it.
You cannot modify a collection inside of a foreach around it.
Instead, you should use a backwards for loop.
If you want to remove Elements from a loop on a list of Elements, the trick is to use a for loop, start from the last Element and go to the first Element.
In your example :
int t_size = table.Rows.Count -1;
for (int i = t_size; i >= 0; i--)
{
DataRow row = table.Rows[i];
// your code ...
}
Edit : not quick enough :)
Also, if you depend on the order that you process the rows and a reverse loop does not work for you. You can add the rows that you want to delete to a List and then after you exit the foreach loop you can delete the rows added to the list. For example,
foreach (DataTable table in JobsDS.Tables)
{
List<DataRow> rowsToRemove = new List<DataRow>();
foreach (DataRow row in table.Rows)
{
if (row["IP"].ToString() != null && row["IP"].ToString() != "cancelled")
{
string newWebServiceUrl = "http://" + row["IP"].ToString() + "/mp/Service.asmx";
webService.Url = newWebServiceUrl;
string polledMessage = webService.mpMethod(row["IP"].ToString(), row["ID"].ToString());
if (polledMessage != null)
{
if (polledMessage == "stored")
{
//removeJob(id);
rowsToRemove.Add(row);
}
}
}
}
rowsToRemove.ForEach(r => removeJob(r["ID"].ToString()));
}
Somehow removeJob(id) changes one of the IEnumerables your enumerating (table.Rows or JobsDS.Tables, from the name of the method I guess it would be the latter), maybe via DataBinding.
I'm not sure the backwards for is going to work directly because it seems you're removing an element enumerated in the outer foreach from within the inner foreach. It's hard to tell without more info about what happens in removeJob(id).