Can you use if statements in .nest(). If not what is the best way to assign labels to array elements so they fit in several groups - d3.js

Question

Is it possible to use if statements within .nest()? I'm trying to populate a column with several keys, but instead of looking for a name I want to assign a name/value to individual rows based on whether the value in the column is within a certain range of numbers. I have looked at the D3 Nest Tutorial and examples and I'm still having a hard time. This is the code I have at the moment, which isn't working. Any help would be greatly appreciated!
fireballData.forEach( d => {
years.forEach(year => {
const latitude = d['Latitude (deg.)'];
const impactEnergy = d['Calculated Total Impact Energy (kt)'];
const impactTest = +impactEnergy;
const impactLevel = nest('impactTest')
.key(function(d) { if (d.impactTest < .5) {return "impactA" }});
// .sortKeys(d3.ascending)
// .key(function(d) { return d.impactEnergy; })
// .sortKeys(function(a,b) {
// return impactEnergy.indexOf(a) - impactEnergy.indexOf(b); })
// .sortValues(function(a,b) { return ((a.who < b.who)
// ? -1
// : 1);;
const longitude = d['Longitude (deg.)'];
const impactYear = d['PeakBrightnessDate_TimeUT'];
const row = {
//year,
impactLevel,
impactEnergy,
latitude,
longitude,
impactYear
};
console.log(row);
});
});
Just to be a bit more clear, I want to assign five or six impact levels to the column impactLevel based on how big of a value impactEnergy is. This would then leave each row with the impactLevel id (ie impactLevel1) followed by the rest of data of that object. Any solustions or suggestions are great appreciated! I am still very new to d3 and I am still learning the in's and out's.

Answer 1

So for what I was trying to accomplish using .nest wasn't a good solution. The better way of going about creating the new array was to use .map.
export const loadAndProcessData = () =>
Promise
.all([
csv('data.csv')
])
.then(([fireballData]) => {
const minYear = 2015;
const maxYear = 2100;
const years = range(minYear, maxYear + 1);
const data = [];
// Special thanks to Darshit Shah for helping me figure this bit out
const showData = fireballData.map(d =>{
const impactYear = d['PeakBrightnessDate_TimeUT'];
const latitude = d['Latitude (deg.)'];
const longitude = d['Longitude (deg.)'];
const impactEnergy = +d['Calculated Total Impact Energy (kt)'];
const target = impactEnergy;
const type = 'Impact Year: ' + impactYear + ', Latitude: ' + latitude + ', Longitude: ' + longitude;
return {
sorce: (impactEnergy < 0.15 ? "0-0.15" : (impactEnergy < 0.25 ? "0.15-0.25" : (impactEnergy < 0.5 ? "0.25-0.5" : ">0.5"))),
target,
type
}
});
data.push(showData);
return data;
`