Question

I have a DataTable like this

name     age
------------
kumar    27
kiran    29
anu      24
peter    34
tom      26
manu     35
sachin   37
geetha   23

Now I have another DataTable like this with one column:

name
----
manu
tom
anu

I need to compare the value in the column name here and remove all the rows that share the same name. Now the result output should be like this:

name     age
------------
kumar    27
kiran    29
peter    34
sachin   37
geetha   23

How can I achive this result?

Answer 1

Assuming you mean .NET datatables and not SQL tables. One approach is the following. Convert your second datatable to a dictionary, something like this:

// create a lookup table to ease the process
Dictionary<string, string> dict = (from row in removeNames.AsEnumerable()
                                   select (string) row["name"])
                                  .ToDictionary(k => k);

You must loop from end to first, otherwise you get problems (cannot use foreach here, it’ll throw an exception).

// loop top to bottom
for(var i = firstDT.Rows.Count - 1; i >= 0; i--)
{
    var row = firstDT.Rows[i];
    if(dict.Exists((string) row["name"]))
    {
        firstDT.Remove(row);
    }
}

---

Edit: better solution

Partially inspired by a little discussion with Jerod below, I figured there had to be a way to do this with a LINQ expression that’s easy to read and apply. Previously, it didn’t work, because I enumerated the DataRowView itself, which, when you try to remove something, will raise an InvalidOperationException, telling you that the collection was modified. Here’s what I did, and it works because we use Select to create a copy of the row items:

// TESTED, WORKS
// assuming table contains {name, age} and removeNames contains {name}

// selecting everything that must be removed
var toBeRemoved = from row in table.Select()
                  join remove in removeNames.AsEnumerable()
                    on row["name"] equals remove["name"]
                  select row;

// marking the rows as deleted, this will not raise an InvalidOperationException
foreach (var row in toBeRemoved)
    row.Delete();