Trying to calculate compound interest in my aggregation query.
I have created this array of weekly return factors, and assuming a starting value of $100
{
"investThis": 100,
"wklyReturns" : [
0.953268776798189,
1.00703473704638,
0.994451681381773,
1.05357596706145,
0.99028490888956,
0.981037037037037,
1.01519025417356,
0.990515443440262,
1.01512249218671,
1.01603072983355,
0.991167064317986,
0.919182492650833,
0.991854491599945,
0.971319397617442,
...
]
}
All need to do is multiply "investThis" by index 0 return factor, then reuse the result and multiply that by index 0+1 return factor, all the way down the weeklyReturns list.
Here are a couple screenshots from google sheet calculation...
Any help is greatly appreciated ๐
If I understand correctly, all you need to do is add your aggregation one more step:
{
$project: {
"results": {
$reduce: {
input: "$wklyReturns",
initialValue: "$investThis",
in: {
$multiply: [
"$$value",
"$$this"
]
}
}
}
}
}
As you can see on the playground.
The $reduce operation allows you to repeat an action each time using the previous result.