Using the Previous Row in a Calculator Formula

Question

Hello.  I am using the calculator to create a new channel that is a custom filtered version of an existing channel.  Unfortunately, I have not been able to identify the previous row entry in the channel.  To make things easier, let's say my filter is a simple averager.  Here is simple pseudocode for what I want to do:
New_Channel = (Existing_Channel[n] + Existing_Channel[n-1]) / 2
where n is the current row.
This is the calculator formula I have come up with:
ch("[1]/New_Channel") = (CHD(chnRow - 1, "[1]/Existing_Channel") + ch("[1]/Existing_Channel")) / 2 + CTNV(chnRow > 1)
Unfortunately, I think chnRow only returns 0.
Obviously, I am a beginner.  I am open to other approaches to creating a new channel with a custom filter. 
Thanks!
Solved!
Go to Solution.

Answer 1

Hi jbuttron,
What you need to do is to copy the channel and delete the first value from the copied channel-- then the Nth row of the original channel will line up with the (N-1)th row of the copied channel.  You should also add the last value of the copied channel to the end of that channel as a new value so both channels end up with the same channel length.  Now you can reference the channels with Ch("[1]/old") and Ch("[1]/new") in the channel calculator expression, assuming that the channel names are "old" and "new" respectively and that both are in the first group.  You don't need a row variable in the expression now, which is good because there's no way to iterate a row variable in a channel calculator expression.  The row iteration is implicit in the channel referencing Ch("[1]/new").
Brad Turpin
DIAdem Product Support Engineer
National Instruments