Compare current and previous row in Java Knime

[sujitnath84]

I am using the java snippet (simple) node. I want to compare the current and just the previous row value. How do I do that?
Like if table is
Row Header
1 A
2 A
3 B
4 C
5 D

When I am in row 2, I want to compare it with row 1, when in row 4, want to compare with row 3 and son on.
Please help!!

[HansS]

Hi @sujitnath84 and welcome to KNIME Forum

Did you try the Lag Column node?
gr. Hans

[sujitnath84]

Yes, tried that now. seems to work.
In Java, there’s no way to reference the previous node? As even if I create an array of the row, it will treat individual row of that column as one array element and it wont go ahead of a[0].
Seems, it works in a much different way than traditional java.

[qqilihq]

It’s possible, though rather crude. I suggest to have a look here:

Java Node Loop over Rows

I have a class of tricky data management problems where the current value of a cell does depend on the value of previous cells in the same column as well as on previous values of other columns. I could do this with first using a “Lag Column” node and thereafter a combination of “Rule Engine”/“Math Formula” or I could pipe the whole thing to R do the transformation there and than pipe it back to Knime. While the Knime solution might work it is not very flexible. The R solution on the other hand…