Case insensitive Arraylist.indexof search

  • Thread starter Thread starter JohnR
  • Start date Start date
J

JohnR

I have an arraylist of string values. I would like to search the arraylist
to find the index of a particular string and I would like the search to be
case insensitive.

dim al as new arraylist
al.add("one")
al.add("two")

dim x as integer = al.indexof("ONE") I would like this to find the match
and return 0

Is there a way to make this happen?

John
 
There is no way i know of that allows you to do a textual compare on
aray objects unfortunatly. You could use the command lcase or ucase to
convert both strings to lower or upper case before you compare.

example:

dim al as new arraylist
al.add("one")
al.add("two")

dim x as integer = al.indexof(lcase("ONE"))

but in this case, if you have al.add("oNe") then i guess it wont work.
you could always do al.add(lcase("oNe")).

or you could use this simple search pattern instead to overcome that
problem. hopefully your arraylist isnt too big, otherwise this would
take a while.

Public al As Collections.ArrayList
Private obj As Object
Private strtest As String
Private indexof As Integer

Public Sub mysub()
al.Add("hello")
strtest = "HeLLo"

For Each obj In al
If LCase(CStr(al.Item(al.IndexOf(obj)))) = LCase(strtest) Then
indexof = al.IndexOf(obj)
End If
Next
End Sub


Please dont hit me if it doesnt work. i havnt tested it!

Hope this helps. Matt
 
Oops. that loop wont finish when its supposed to.

after the line: indexof = al.IndexOf(obj)
you will to put: exit for
 
If it doesn't mattter that the items are sorted after you've added them you
can use the CaseInsensitiveComparer and binarysearch, but this only works if
you sort the arraylist with the same
Icomparer(CaseInsensitiveComparer.Default) as you want to use for your
binarysearch.

Hth Greetz Peter

Dim arrList As New ArrayList

arrList.Add("One")
arrList.Add("tWo")
arrList.Add("thRee")
arrList.Sort(CaseInsensitiveComparer.Default)
MsgBox(arrList.BinarySearch("three",
CaseInsensitiveComparer.Default))
 
Thanks, Peter. I didn't think of that.

John

Peter Proost said:
If it doesn't mattter that the items are sorted after you've added them
you
can use the CaseInsensitiveComparer and binarysearch, but this only works
if
you sort the arraylist with the same
Icomparer(CaseInsensitiveComparer.Default) as you want to use for your
binarysearch.

Hth Greetz Peter

Dim arrList As New ArrayList

arrList.Add("One")
arrList.Add("tWo")
arrList.Add("thRee")
arrList.Sort(CaseInsensitiveComparer.Default)
MsgBox(arrList.BinarySearch("three",
CaseInsensitiveComparer.Default))
Click to expand...
 
Hi Ken,

I tried option Compare but it didn't work for the IndexOf which gets
evaluated in the object.equals method.

Ron
 
Just curious as to why you have to sort the arraylist first...trying to learn
all I can and don't undetstand?
 
Hi Dennis, is far as I remember, you have to do it because otherwise you can
get the wrong index returned.
Or as stated in the msdn:

"If comparer is provided, the elements of the ArrayList are compared to the
specified value using the specified IComparer implementation. If the
ArrayList is not already sorted according to the sort order defined by
comparer, the result might be incorrect."

you can try it for yourself, if you remove the
arrList.Sort(CaseInsensitiveComparer.Default) from my small example you
should get the wrong result.

Hth Greetz Peter
 
Dennis,
Because ArrayList.BinarySearch is only defined on sorted lists.

http://msdn.microsoft.com/library/d...ollectionsArrayListClassBinarySearchTopic.asp

The reason ArrayList.BinarySearch is only defined on sorted lists is because
the Binary Search algorithm is "optimally" defined on sorted lists.

For details on the Binary Search algorithm see:

http://www.nist.gov/dads/HTML/binarySearch.html

http://en.wikipedia.org/wiki/Binary_search

--
Hope this helps
Jay
T.S. Bradley - http://www.tsbradley.net


| Just curious as to why you have to sort the arraylist first...trying to
learn
| all I can and don't undetstand?
| --
| Dennis in Houston
|
|
| "Peter Proost" wrote:
|
| > If it doesn't mattter that the items are sorted after you've added them
you
| > can use the CaseInsensitiveComparer and binarysearch, but this only
works if
| > you sort the arraylist with the same
| > Icomparer(CaseInsensitiveComparer.Default) as you want to use for your
| > binarysearch.
| >
| > Hth Greetz Peter
| >
| > Dim arrList As New ArrayList
| >
| > arrList.Add("One")
| > arrList.Add("tWo")
| > arrList.Add("thRee")
| > arrList.Sort(CaseInsensitiveComparer.Default)
| > MsgBox(arrList.BinarySearch("three",
| > CaseInsensitiveComparer.Default))
| >
| > --
| > Programming today is a race between software engineers striving to build
| > bigger and better idiot-proof programs, and the Universe trying to
produce
| > bigger and better idiots. So far, the Universe is winning.
| >
| >
| > "Matt" <[email protected]> schreef in bericht
| > | > > Oops. that loop wont finish when its supposed to.
| > >
| > > after the line: indexof = al.IndexOf(obj)
| > > you will to put: exit for
| > >
| > >
| > > Matt wrote:
| > > > There is no way i know of that allows you to do a textual compare on
| > > > aray objects unfortunatly. You could use the command lcase or ucase
to
| > > > convert both strings to lower or upper case before you compare.
| > > >
| > > > example:
| > > >
| > > > dim al as new arraylist
| > > > al.add("one")
| > > > al.add("two")
| > > >
| > > > dim x as integer = al.indexof(lcase("ONE"))
| > > >
| > > > but in this case, if you have al.add("oNe") then i guess it wont
work.
| > > > you could always do al.add(lcase("oNe")).
| > > >
| > > > or you could use this simple search pattern instead to overcome that
| > > > problem. hopefully your arraylist isnt too big, otherwise this would
| > > > take a while.
| > > >
| > > > Public al As Collections.ArrayList
| > > > Private obj As Object
| > > > Private strtest As String
| > > > Private indexof As Integer
| > > >
| > > > Public Sub mysub()
| > > > al.Add("hello")
| > > > strtest = "HeLLo"
| > > >
| > > > For Each obj In al
| > > > If LCase(CStr(al.Item(al.IndexOf(obj)))) =
LCase(strtest)
| > Then
| > > > indexof = al.IndexOf(obj)
| > > > End If
| > > > Next
| > > > End Sub
| > > >
| > > >
| > > > Please dont hit me if it doesnt work. i havnt tested it!
| > > >
| > > > Hope this helps. Matt
| > > >
| > > > JohnR wrote:
| > > >
| > > >> I have an arraylist of string values. I would like to search the
| > > >> arraylist to find the index of a particular string and I would like
| > > >> the search to be case insensitive.
| > > >>
| > > >> dim al as new arraylist
| > > >> al.add("one")
| > > >> al.add("two")
| > > >>
| > > >> dim x as integer = al.indexof("ONE") I would like this to find
the
| > > >> match and return 0
| > > >>
| > > >> Is there a way to make this happen?
| > > >>
| > > >> John
| > > >>
| >
| >
| >
 
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