How can I perform rolling operations without a fixed window size?

I have a table of data where I'd like to calculate some rolling metrics. However, instead of a fixed window size, I'd like the rolling metrics to be based on values in another column. When I see a particular value in the other column, I want the metrics to reset. How can I do this?

You can accomplish this with an update or an update_view and two update_by operations. Say, for instance, you have a source table with two columns: Value and Sym. You want to calculate the running sum of Value, but have that sum reset every time DesiredValue occurs in Sym. A solution would look something like this:

result = source.update_view(["Counter = Sym == `DesiredValue`"]).update_by(
    ops=cum_sum(["SumValue = Value"], by=["Counter"])
)

note

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