Adjacent Record Mapping

Overview

Examples Calculating a set of returns.

let data = [{value:1},{value:2},{value:3},{value:4},{value:5}];
let results = data.map((p,i, data)=>{
  let item = {
    value:p.value,
	return:null
  };
  if(i>0) item.return = p.value/data[i-1].value;
  return item;
});
				

Try it!