C#:
I have a datatable with a variable number of columns - returned by calling a stored procedure.
and I would like to convert it to Dictionary key-value pairs (string).
How do I achieve this without having to iterate through each column in each row? I won't know how many columns are there in the datatable at any time.
Thanks
G
You said your result should contain values for the first (and only) row of the dataTable
This one liner can do the trick
var res = dt.Columns.Cast<DataColumn>().ToDictionary(col => col.ColumnName, col=>dt.Rows[0][col]);
ToDictionary will internally enumerate the columns
But I really prefer this explicit enumeration:
var row = dt.Rows[0];
var res2 = new Dictionary<string, object>();
foreach (DataColumn col in dt.Columns)
res2.Add(col.ColumnName, row[col]);
The second is much more readable IMHO.
You can use a method like this calling the extension method ToDictionary() :
internal Dictionary<string,object> GetDict(DataTable dt)
{
return dt.AsEnumerable()
.ToDictionary(row => row.Field<string>(0),
row => row.Field<object>(1));
}
Related
This question already has answers here:
Remove Single Quotes From All Cells in a DataTable - Creating New Table - Using LINQ in Vb.Net
(2 answers)
Closed 3 years ago.
How to replace double quotes of all rows of DataTable using Linq in C#?
I tried below but I need more optimized code for same purpose
int columnIndex = 0;
dtExcelData.Rows.RemoveAt(0);
foreach (DataColumn excelSheetColumns in dtExcelData.Columns)
{
int rowIndex = 0;
foreach (DataRow row in dtExcelData.Rows)
{
dtExcelData.Rows[rowIndex][columnIndex] = dtExcelData.Rows[rowIndex][columnIndex].ToString().Replace("\"", "");
rowIndex++;
}
columnIndex++;
}
Please suggest
You could make use of DataRow.ItemArray. For example
foreach(var row in dtExcelData.Rows.Cast<DataRow>())
{
row.ItemArray = row.ItemArray.Select(x=>x.ToString().Replace("\"","")).ToArray();
}
You should
be aware you remove the first row, if you write results back to your data store you will lose this row.
ask yourself why you iterare over Columns and rows if you never use the objects. Why don't you simply use a for loop over rowIndex and columnIndex.
think about only processing data fields that really are a string.ToString() turns everything into a string, then you overwrite any kind of data field type with a string. Better test for "is String" and then cast the field into (String).
think about getting every row, then process every column in this row. This could be faster to execute, but even if it isn't then still is more understandable (at least to me).
I have added code here because code is better other than URL, You can try this below code:
That is already mentioned in below URL
Remove Single Quotes From All Cells in a DataTable - Creating New Table - Using LINQ in Vb.Net
dtExcelData.Rows.RemoveAt(0);
DataTable clone = dtExcelData.Clone();
string t;
var qry = from DataRow row in dtExcelData.Rows
let arr = row.ItemArray
select Array.ConvertAll(arr, s =>
(t = s as string) != null
&& t.StartsWith("\"")
&& t.EndsWith("\"") ? t.Trim('\"') : s);
foreach (object[] arr in qry)
{
clone.Rows.Add(arr);
}
I'm trying to use LINQ on DataTable that's getting it's data from sql. So I have a data table with it's usual columns and rows and it appears exactly like a sql select statement. Now I need to get certain rows and columns (including column names) from this data.
I converted the datatable to something LINQ can use using AsEnumerable but I'm not sure what exactly it does. Does it convert the data into an array of objects where each row becomes an object?
I'm used to working with Javascript and it's newer arrow functions so i'd like to use Linq with lambda to keep it consistent.
I'm trying to get rows and column names where first column has a value equal to 2018
DataTable myTable = getData(); // populates the datatable and I've verified the data
var linqTable = myTable.AsEnumerable().Select( x => x[0] = 2018);
I need to get the rows and column names. e.g like an object or array of objects.However, the code above doesn't return the data or column names but just two rows with 2018 in it.
My goal is to eventually serialize this data as json and send it to web page.
To Get the column names:
myTable.Columns.Cast<DataColumn>().Select(dc =>dc.ColumnName).ToList();
The problem is Select() is projecting the objects into a new form. You are seeing 2018 because of '=' instead of '=='. You need to use Where()
var linqTable = myTable.AsEnumerable().Where( x => x.Field<int>(0) == 2018);
You will still end up with a list of DataRows though. The DataTable object isn't really what you should be using because it already provides a nice way to filter its rows:
myTable.Rows.Find(2018);
If you are trying to convert it to a list of objects you should use the Select() method something like:
var linqTable = myTable.AsEnumerable().Where(x => x.Field<int>(0) == 2018)
.Select(x => new
{
year = x[0],
p1 = x[1],
p2 = x[2] // etc...
});
You can create the following function:
public static DataTable CreateDataTableFromAnyCollection<T>(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,null);
}
dataTable.Rows.Add(values);
}
return dataTable;
}
and pass any type of object your LINQ query returning.
DataTable dt = CreateDataTableFromAnyCollection(query);
I hope this will help you.
Creating a DataTable From a Query (LINQ to DataSet)
I see a lot of complex examples for converting a DataTable with multiple-member rows here but in my case, the query simply returns one column from a table, that is to say 0..N strings/varchars, such as:
bbfinaleofseem#wallacestevens.org
eyenoy#dunbar.com
I thought something like this should work:
DataTable UnitReportPairEmailValsDT = new DataTable();
string qry = string.Format(SQL.UnitReportPairEmailQuery, unit, rptId);
UnitReportPairEmailValsDT = SQL.ExecuteSQLReturnDataTable(
qry,
CommandType.Text,
null
);
List<String> emailAddresses = new List<string>();
foreach (string emailaddr in UnitReportPairEmailValsDT)
{
emailAddresses.Add(emailaddr);
}
...but it won't compile ("foreach statement cannot operate on variables of type 'System.Data.DataTable' because 'System.Data.DataTable' does not contain a public definition for 'GetEnumerator'")
I tried appending ".AsEnumerable" to "in UnitReportPairEmailValsDT" too, but that also provoked the wrath of the compiler.
Error says you cannot loop through DataTable object itself, probably what you need is looping through DataRows.
Use this.
foreach(DataRow row in UnitReportPairEmailValsDT.Rows)
{
emailAddresses.Add(row["emailaddr"].ToString()); // assuming you have emailaddr column.
}
Other option, use Linq
emailAddresses = UnitReportPairEmailValsDT
.AsEnumerable()
.Select(row=> row.Field<string>("emailaddr"))
.ToList();
try something like this:
List<String> emailAddresses = new List<string>();
foreach (DataRow row in UnitReportPairEmailValsDT.Rows)
{
emailAddresses.Add(row.Item(0));
}
Suppose dt is your data table then using Linq:
dt.Rows.Select(x=> x[0]+"").ToList() will give you List. Beware of using Select(x=>xToString()) as it is prone to error if column value is null. x[0]+"" makes sure that in case of null empty string is returned.
I'm trying to perform the C# equivalent of Select * where [columnname] = [value]. I began with a foreach loop to iterate through the table row by row, however I had forgotten that one cannot access a column via row.column["<colname>"].
How do I achieve this objective? Most of the examples I have seen target one specific row with the intention of casting it's value to a string, however my task is to move all entries with a value of DateTime == < DateTime.Today to an archived table.
Can I continue with the following code? Or am I approaching this in the wrong manner?
void archiveDates()
{
foreach (DataRow row in workingupdates.storageTable.Rows)
{
//target DateTime column here
}
}
You can use the Field extension method that is strongly typed and also supports nullable types. You have an overload for the index, name or the DataColumn(among others):
foreach (DataRow row in workingupdates.storageTable.Rows)
{
DateTime dt = row.Field<DateTime>("columnname");
}
If you instead want to find all rows where the date column has a specific value you can use Linq-To-DataTable:
var matchingDataRows = workingupdates.storageTable.AsEnumerable()
.Where(row => row.Field<DateTime>("columnname") == dateTimeVariable);
Now you can simply enumerate this query:
foreach (DataRow row in matchingDataRows)
{
// ...
}
Or create a collection like
a DataRow[] with matchingDataRows.ToArray() or
a List<DataRow> with matchingDataRows.ToList()
a new DataTable with matchingDataRows.CopyToDataTable()
Note that you have to add System.Linq; to the top of the file.
I'm using ADO.NET and C#, and I want to convert a DataTable object into an array of DataRows. What is an elegant way of doing this?
My first question would be why? The request makes no sense.
The answer is:
DataRow[] rows = myDataTable.Select();
Actually the DataTable has a property called Rows, witch provides the methods to do this.
You can accomplish this doing:
List<System.Data.DataRow> r = d.Rows.AsQueryable().OfType<System.Data.DataRow>().ToList();
DataTable.Select() gives you an array of DataRows. You can use this as an array
Dim dt As New DataTable
Dim dr() As DataRow = dt.Select()
In case you want an ArrayList, you can
public ArrayList ConvertDT(ref DataTable dt)
{
ArrayList converted = new ArrayList(dt.Rows.Count);
foreach (DataRow row in dt.Rows)
{
converted.Add(row);
}
return converted;
}
I have not used the dt.rows.CopyTo function. maybe that works also.
If you would like to see the contents as a string, use this code:
string.Join(",", dataTable.AsEnumerable().SelectMany(row => row.ItemArray))