I would like to know how I can convert elements of a column of a DataTable to a list of type string, grouping the elements to avoid repetition.
For example my DataTable would look like this
DataTable
and I want to make a list containing the elements of only "User" without repeating itself using LINQ.
The code I was trying to use is
InvoiceList = InvoiceDT.AsEnumerable().GroupBy(Function(r) r("User").ToString).ToList(Function(g) g.ToList())
But it doesn't work for me since I am new to LINQ and still have problems forming the structures.
I'd use this:
InvoiceList = InvoiceDT.AsEnumerable().Select(Function(r) r("User").ToString()).Distinct().ToList()
If you wanted a GroupBy solution it's
InvoiceList = InvoiceDT.AsEnumerable().GroupBy(Function(r) r("User").ToString()).Select(Function(g) g.Key).ToList()
Where your code went wrong was in trying to pass a delegate to ToList; it doesn't take one (and you wouldn't ToList the g either, as it's a list of data rows with all varying properties).
To reshape our IGrouping (something like a list of objects that all share the same Key, which is a property of the list that the IGrouping represents) produced by the groupby into a sequence of string Keys we Select the Key, and then ToList that
There is a lot of back and forthing between developers over things like ToList vs ToArray - some people universally use ToList because, for collections of an unknown number of elements, both list and array will grow and resize repeatedly in the same way but using ToArray requires one additional resizing step at the end to trim off any unused slots. Mostly that's trivial in terms of an overall performance consideration and should be weighed against the benefit of releasing the memory with the trim. Getting into finer details is way beyond the scope of this answer but you can read some huge blog posts about it.
I personally think it's more important to generate sensible code by calling the method that results in the relevant type depending on what you plan to do with it; I ToList if I need List functionality (add/insert/remove).. I prefer ToArray if an array suits the follow-on purposes (read/write/random access, no insert or delete), and if I'll only ever enumerate it I don't To... anything at all - I just ForEach the result of the query, which can give a bigger performance boost than anything else because it means I may not have to enumerate the entire set (if I stop early) or allocate memory all at once for doing so (if I'm writing to a socket or file)
On the use of ToString; it's worth avoiding if you think you'll fall into a pattern where you do it on every column just to get a string. If the column is already a string it's an acceptable way to get the object that DataRow.Item gives you, into a string. If the column is another type it's better to cast it:
DirectCast(r("Age"), Integer)
r.Field(Of Integer)("Age")
Thing is, it's verbose, and ugly, and intellisense doesn't help you out with writing Age or knowing it's an Int. LINQ in VB is bad enough for verbosity without pouring gas on that fire. If you're working with datatables of a known structure, it's a lot nicer if you make strongly typed ones:
Add a new file of type DataSet to your project
Open it so the design surface appears. In the properties grid call it something reasonable, such as AccountsDataSet
Right click, Add Table, call it Invoices
Right click the emppty table, Add Column, call it User
Then use it like:
Dim dt as new AccountsDataSet.InvoicesDataTable
Populate it like:
dt.AddInvoicesRow("John Smith", ... other properties here)
Query it like:
dt.Select(Function(r) r.User).Distinct()
Much nicer than accessing column names by string, and having them be objects that need casting..
Consider the dataset generator as a way to quickly, visually, create poco classes with named, typed properties
Try this
dim list as List(of string) = InvoiceDT.Rows.
Cast(of DataRow)().
Select(Function(r) r("User").ToString()).
Distinct().
ToList()
Here you cast Row collection as IEnumerable(of DataRow), rest is trivial
I've looked through a number of tutorials and asks, and haven't found a working solution to my problem.
Suppose my dataset has two columns: sort_order and field_value. sort_order is an integer and field_value is a numerical (10,2).
I want to format some rows as #,#0 and others as #,#0.00.
Normally I would just do
iif( fields!sort_order.value = 1 or fields!sort_order.value = 23 or .....
unfortunately, the list is fairly long.
I'd like to do the equivalent of if fields!sort_order.value in (1,2,21,63,78,...) then...)
As recommended in another post, I tried the following (if sort in list, then just output a 0, else a 1. this is just to test the functionality of the IN operator):
=iif( fields!sort_order.Value IN split("1,2,3,4,5,6,8,10,11,15,16,17,18,19,20,21,26,30,31,33,34,36,37,38,41,42,44,45,46,49,50,52,53,54,57,58,59,62,63,64,67,68,70,71,75,76,77,80,81,82,92,98,99,113,115,116,120,122,123,127,130,134,136,137,143,144,146,147,148,149,154,155,156,157,162,163,164,165,170,171,172,173,183,184,185,186,192,193,194,195,201,202,203,204,210,211,212,213,263",","),0,1)
However, it doesn't look like the SSRS expression editor wants to accept the "IN" operator. Which is strange, because all the examples I've found that solve this problem use the IN operator.
Any advice?
Try using IndexOf function:
=IIF(Array.IndexOf(split("1,2,3,4,...",","),fields!sort_order.Value)>-1,0,1)
Note all values must be inside quotations.
Consider the recommendation of #Jakub, I recommend this solution if
your are feeding your report via SP and you can't touch it.
Let me know if this helps.
I'm currently making a game for an Advanced Higher computing course. After having my previous question answered perfectly and helping me a great bunch. I was wondering if you could share you wisdom upon me once again...
I've currently declared the variables, got the selection process narrowed down. All I'm sturggling to do is for it to recognise it's a variable and not the location itself.
UsedTile = My.Resources.Token(Turn)
CurrentTile = My.Resources.Colour(Turn)
I should also mention that UsedTile and CurrentTile are declared as Image so that it works with the rest of my progam.
Token is an array that swaps between 1 & 2 which is defined by Turn.
Sorry if i'm explaining this baddly, but basically I would want it to look something like
UsedTile = My.Resources.(Colour(Turn))
So that it is interchangable. All of the reasources are there, so for instance it would be a red tile it should show as
UsedTile = My.Resources.ColourRed.png
Thanks, I hope I've made it understandable. I'd happily upload more code if needed :)
-Lewis
It's a little unclear what it is that you are asking, but here are two suggestions that may help you. First, you may want to consider reading the resources once and storing them in some other data structure that makes them more convenient to access when you need them later. For instance, if you created a class like this:
Public Class ColourResources
Public Property TurnImages As Image(2)
End Class
Then you could create an array of them and fill them like this:
Dim colors(2) As ColourResources
colors(0).TurnImages(0) = My.Resources.ColourRed
colors(0).TurnImages(1) = My.Resources.ColourRedUsed
colors(1).TurnImages(0) = My.Resources.ColourBlack
colors(1).TurnImages(1) = My.Resources.ColourBlackUsed
Then when you need a particular image, you could just access in some way similar to this:
Dim tile As Image = colors(currentColor).TurnImages(currentTurn)
If your colors and turns are kept track of with some data type other than an Integer, you could use dictionaries instead of arrays.
My second suggestion is that it is possible to get the resource by string name rather than via resource-designer-auto-generated property. For instance, instead of this:
UsedTile = My.Resources.ColourRed
You could also access the same image like this:
UsedTile = DirectCast(My.Resources.ResourceManager.GetObject("ColourRed"), Image)
Depending on your needs, that may be useful to you.
I'm just looking to be able to sort the results of a BatchedJoinBlock (http://msdn.microsoft.com/en-us/library/hh194683.aspx) so that the different results of the different targets stay together. I will explain! Example in some pseudo-code:
Dim batchedJoin = New BatchedJoinBlock(Of String, object)(4)
batchedJoin.Target1.Post("String1Target1")
batchedJoin.Target2.Post(CType(BuildIt, StringBuilder1))
batchedJoin.Target1.Post("String1Target2")
batchedJoin.Target2.Post(CType(BuildIt, StringBuilder2))
Dim results = batchedJoin.Receive()
'This sorts one result...
Dim SortByResult = results.Item1.OrderBy(Function(item) item.ToString, New NaturalStringComparer)
Basically I've got a string and an object, the SortByResult variable above sorts the strings exactly as I'd like them to sort. I'm looking for a way to get the objects that used to be at the same index number in target2 into the same order. e.g. if "String1Target1" changes order I'd like to somehow reliably refer to/pair it together with "StringBuilder1". The actual end result just needs to be that the objects (target2) are sorted in the order that is dictated by the strings being sorted (target1). Something like:
Dim EndResult = results.Item2.OrderBy(strings in target1)
but I'll gladly take an intermediate solution! I've also tried using a dictionary (results.Item2.ToDictionary) with the string as a key (which would also be a fine solution) but it's a bit beyond my ken using lamba expressions in the proper context. I can realistically do this in several steps with a list or something, but I'm trying to get something more efficient/learn something, and it seems like there's a lot of default options with the results of the jointblock that I'm just not experienced enough to use. Thanks in advance for any help you can provide!
To me, it looks like you don't actually want BatchedJoinBlock, because the two pieces of data always come together. A better option for that would be a BatchBlock of Tuple<string, object>. When you have that, you can then use LINQ directly to sort each batch:
results.OrderBy(Function(tuple) tuple.Item1)
Here is the single line from one of my functions to test if any objects in my array have a given property with a matching value
Return ((From tag In DataCache.Tags Where (tag.FldTag = strtagname) Select tag).Count = 1)
WHERE....
DataCache.Tags is an array of custom objects
strtagname = "brazil"
and brazil is definitely a tag name stored within one of the custom objects in the array.
However the function continually returns false.
Can someone confirm to me that the above should or should not work.
and if it wont work can someone tell me the best way to test if any of the objects in the array contain a property with a specific value.
I suppose in summary I am looking for the equivalent of a SQL EXISTS statement.
Many thanks in hope.
Your code is currently checking whether the count is exactly one.
The equivalent of EXISTS in LINQ is Any. You want something like:
Return DataCache.Tags.Any(Function(tag) tag.FldTag = strtagname)
(Miraculously it looks like that syntax may be about right... it looks like the docs examples...)
Many Thanks for the response.
Your code did not work. Then I realised that I was comparing to an array value so it would be case sensitive.
However glad I asked the question, as I found a better way than mine.
Many thanks again !