line.x([x])
If x is specified, sets the x accessor to the specified function or number and returns this line generator. If x is not specified, returns the current x accessor, which defaults to:
function x(d) {
return d[0];
}
When a line is generated, the x accessor will be invoked for each defined element in the input data array, being passed the element d, the index i, and the array data as three arguments. The default x accessor assumes that the input data are two-element arrays of numbe