IRR
Description 
Internal rate of return (IRR) is a metric of profitability for potential investments. Internal rate of return is a discount rate that sets the net present value (NPV) of all future cash flows the investment equal to zero. An approximate solution is found using numerical iteration. 
Signature 
IRR(Node [, Guess]) 
Parameters 

Example
We have project with following cashflows.
'CF'=
Year  CF 

2018  10000 
2019  1155 
2020  5000 
2021  7000 
Our goal is to find a discount rate with which the discounted cash flows sumup to zero:
IRR('CF')=
Year  Totals 

2020  23% 
2021  12% 
The IRR function tells us the rate is 12%. The result for Cash Flows up to year 2020 is not interesting for us and can be filtered out with FILTER function.