histogram.thresholds()

histogram.thresholds([count])
histogram.thresholds([thresholds])

If thresholds is specified, sets the threshold generator to the specified function or array and returns this histogram generator. If thresholds is not specified, returns the current threshold generator, which by default implements Sturges’ formula. (Thus by default, the histogram values must be numbers!) Thresholds are defined as an array of values [x0, x1, …]. Any value less than x0 will be placed in the first bin; any value greater than or equal to x0 but less than x1 will be placed in the second bin; and so on. Thus, the generated histogram will have thresholds.length + 1 bins. See histogram thresholds for more information.

If a count is specified instead of an array of thresholds, then the domain will be uniformly divided into approximately count bins; see ticks.