d3.js equivalent to columns in R dataframes - r

Question

I have some data stored in this format (except many cases more):
var data = [
{"name":"John", "team":"team1"},
{"name":"Megan", "team":"team2"},
{"name":"Rupert", "team":"team2"},
{"name":"Albert", "team":"team1"}
];
I want to create this:
var colourScale = d3.scale.ordinal()
.range(a)
.domain(b)
"a" being an array of all levels of "team" (i.e. ["team1","team2"] in this case).
"b" being an array of ordinal colours of the same length as "a".
colourScale() should take the "team"-value as input and return a unique colour for each team.
How do I create "a" and "b"? Is there something equivalent to R's levels(data[ ,"team"]) in javascript or d3.js?

Answer 1

It's not exactly your solution as you don't explicitly find your specified a or b, but I found
var colourScale = d3.scale.category10();
function colour(d) { return d.team; }
and on the object you want to colour, bound to the appropriate data, chain
.style("fill", function(d) { return colourScale(colour(d)); });
has the effect that I assume you're searching for. Hope this helps.

Answer 2

I think there are some extra steps you need to do. You need first to create a 'unique' set of possible domain values. Then you can create a function that maps each value to a color. Something like this perhaps:
// A function to get unique values, can be optimized further
function unique(x) {
return x.reverse().filter(function (e, i, x) {return x.indexOf(e, i+1) === -1;}).reverse();
}
var data = [
{"name":"John", "team":"team1"},
{"name":"Megan", "team":"team2"},
{"name":"Rupert", "team":"team2"},
{"name":"Albert", "team":"team1"}
];
// An arbitrary set of colors
colors = ['#005824','#1A693B','#347B53','#4F8D6B','#699F83','#83B09B','#9EC2B3','#B8D4CB','#D2E6E3','#EDF8FB','#FFFFFF','#F1EEF6','#E6D3E1','#DBB9CD','#D19EB9','#C684A4','#BB6990','#B14F7C','#A63467','#9B1A53','#91003F']
//Create the ordinary scale based on your color set above
colorScale= d3.scale.ordinal()
.domain(unique(data.map(function(d){return d.team;})))
.range(colors)
Then you can access the color by:
.style("fill",function(d){return colorScale(d.team);})
Hope this helps.