Implement cumulative_sum() function #7388
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Can you update the description with more details about the use of this function? |
jsternberg
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Updated the description. |
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| func (r *FloatCumulativeSumReducer) AggregateFloat(p *FloatPoint) { | ||
| if !r.curr.Nil && r.curr.Time == p.Time { |
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What is this logic for? Skipping points in the sum that have the same time? What is the use case?
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All of the other stream processors will skip points at the same time such as derivative() and difference() so I had this one do it too. It's to avoid having it emit multiple values at the same time. I can remove this though. I don't think I have the same thing with moving_average() even though it's also a stream processor. Which do you think is more correct?
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I think we shouldn't skip points in this case. The reason that derivative does it is it needs to use the elapsed time and it would create a divide by 0 otherwise. Since this is just a sum I would rather it simply sum the values and nothing else, similar to moving_avg.
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I would concur with @nathanielc's logic here, if this is meant to be a 'wrapper' function to something like derivative anyway, let the derivative handle the dupes accordingly and simply sum up the reseults it presents. That should keep things easy.
| // FloatCumulativeSumReducer cumulates the values from each point. | ||
| type FloatCumulativeSumReducer struct { | ||
| curr FloatPoint | ||
| emitted bool |
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Emitted doesn't seem to be used anywhere, did I miss something?
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Emitted is used to skip points at the same time value. It is used in Emit().
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@nathanielc I updated this with your recommendation. Can you take another look? |
The `cumulative_sum()` function can be used to sum each new point and
output the current total. For the following points:
cpu value=2 0
cpu value=4 10
cpu value=6 20
This would output the following points:
> SELECT cumulative_sum(value) FROM cpu
time value
---- -----
0 2
10 6
20 12
As can be seen, each new point adds to the sum of the previous point and
outputs the value with the same timestamp.
The function can also be used with an aggregate like `derivative()`.
> SELECT cumulative_sum(mean(value) FROM cpu WHERE time >= now() - 10m GROUP BY time(1m)
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The
cumulative_sum()function can be used to sum each new point andoutput the current total. For the following points:
This would output the following points:
As can be seen, each new point adds to the sum of the previous point and
outputs the value with the same timestamp.
The function can also be used with an aggregate like
derivative().