Help on Union of Arrays

[JPA21]

So I have a problem that says: Write a program that creates a file containing the names of every person who served as either vice-president or president. The program also should display the number of those names in a message box. I also have to create a third array that names every person that served as both. That is where I am having the problem. The rest of it I have figured out. The union of the array is not working. Here is my code:

ublic Class frmAhearnAh
Dim vicePres() As String = IO.File.ReadAllLines("VPres.txt")
Dim presidents() As String = IO.File.ReadAllLines("USPres.txt")
Private Sub btnOr_Click(sender As Object, e As EventArgs) Handles btnOr.Click
Dim eitherOR() As String
eitherOR = (vicePres.Union(presidents))
IO.File.WriteAllLines("OR.txt", eitherOr)
Dim number = eitherOr.Count - 1
MsgBox(number & " people", "File Created")
End Sub
End Class

Thank you for your help in advance!

[jmcilhinney]

You have forgotten your primary school maths. What you want is the intersection of the two sets, i.e. the elements common to both, rather than the union of the two sets, i.e. the elements that are in either one or the other or both.

[JPA21]

Actually no, I am looking for those who served as vice president or president, which would mean everyone on the list, except for duplicates

[jmcilhinney]

Actually no, I am looking for those who served as vice president or president, which would mean everyone on the list, except for duplicates

For some reason I thought I'd read that you said "both" in your post but I see now that I just made that up.

In that case, I'll go back to what I originally was going to post but deleted. It's NEVER adequate to say that something isn't working. ALWAYS explain what you expect to see, what you actually see and how they differ. That way, we know what we're looking for rather than just hoping something jumps out at us.

That said, I don't understand why you're subtracting 1 from the count there. That's exactly the sort of action that should be accompanied by an explanatory comment, i.e. WHY you are seemingly inexplicably subtracting 1 from the count when what you want is the count.

Also, while it won't stop your code working, you should not be using `eitherOr` twice like that. Union uses deferred execution, as so many LINQ methods do, which means that the result is not created when you call Union but when you use that result. By using the result twice, you're actually creating the union twice, which is inefficient. If you want to use the result of a LINQ query multiple times then you should call ToArray or ToList to create an array or collection and then use that multiple times. That way, you won't be performing the query over and over just to get the same result every time.

[Evil_Giraffe]

For some reason I thought I'd read that you said "both" in your post but I see now that I just made that up.

I also have to create a third array that names every person that served as both. That is where I am having the problem. The rest of it I have figured out. The union of the array is not working.

[Shaggy Hiker]

I second EG's confusion.

[techgnome]

Third.... in favor.... Aye!

-tg

[passel]

None of the "solution" seems to jibe with the statement of work.
Requirement: Write a program that creates a file containing the names of every person who served as either vice-president or president.
Interpretation: Write a program that creates one file containing the names of every person who has served as either vice-president or president.
The code is not creating a file, it is reading from two files that must have been previously created.

Dim vicePres() As String = IO.File.ReadAllLines("VPres.txt")
Dim presidents() As String = IO.File.ReadAllLines("USPres.txt")

Requirement: The program also should display the number of those names in a message box.
Interpretation: The messagebox should display the total number of names in the file (of persons who have been either President, Vice President, which would include those that have been both).

I also have to create a third array that names every person that served as both.

Where did that come from? Is that a requirement? Also, if you did fill that array with your code it wouldn't be every person that served as both, but every person who served as either (if you do a Union), so should be the output you're looking for, for your output file and messagebox, assuming the below statement of work is correct.

Probably the full statement of work is:
You are given two files, one lists the names of persons who have served as presidents, the second the names of persons who have served as vice-presidents.
Write a program that creates a file containing the names of every person who served as either vice-president or president.
The program also should display the number of those names in a message box.
Expected Result: The number displayed should be less then the number in the two lists combined as some persons have served as both vice-president and president.

As for the Union line not working, shouldn't that be
eitherOR = vicePres.Union(presidents).ToArray

[jmcilhinney]

I second EG's confusion.

Third.... in favor.... Aye!

-tg

Van Damme! I obviously did read what I thought I read the first time but, when the OP claimed otherwise, I went back to read it again and stopped after this part:

I also have to create a third array that names every person that served as both. That is where I am having the problem. The rest of it I have figured out.

When the OP refuted that, I went back and read the post again but stopped after this part:

Write a program that creates a file containing the names of every person who served as either vice-president or president.

and assumed that I had indeed misread it the first time. I have to stop posting in a hurry.

So, I was right in the first place. If you want a list of those who served as either then you want a union and if you want a list of those who served as both then you want an intersection. Like I said, primary school maths.