It took me a bit to figure out how to do absolute values in RethinkDB, because you can’t use conditionals and mathematical operations that you might normally expect.

I expect that abs will be added to the language relatively soon, based on the outstanding tickets, but if you need it now, here is how to implement it:

```
'aDelta':
r.branch(
row('Delta').gt(0),
row('Delta'),
row('Delta').mul(0)
),
```

The following query is more complete if you want to see an example in action – this computes root-mean-square variance as well (unfortunately there does not appear to be a power function in the language as yet, so you can’t do the square root at the end that you’d want)

```
r.database('performance')
.table('query_timings)
.map(function(row) {
return {
'Delta': row('Delta'),
'aDelta':
r.branch(
row('Delta').gt(0),
row('Delta'),
row('Delta').mul(0)
),
'rmsDelta': row('Delta').mul(row('Delta')),
'Count': 1
}
})
.group('Count')
.reduce(function(left, right) {
var Delta = left('Delta').add(right('Delta'));
var aDelta = left('aDelta').add(right('aDelta'));
var rmsDelta = left('rmsDelta').add(right('rmsDelta'));
var Count = left('Count').add(right('Count'));
return {
Delta: Delta,
Count: Count,
aDelta: aDelta,
rmsDelta: rmsDelta,
Variance: rmsDelta.exp(0.5),
Avg: Delta.div(Count)
}
})
```