in miredot/lib/lunr/js/lunr.js [2187:2211]
lunr.Builder.prototype.calculateAverageFieldLengths = function () {
var fieldRefs = Object.keys(this.fieldLengths),
numberOfFields = fieldRefs.length,
accumulator = {},
documentsWithField = {}
for (var i = 0; i < numberOfFields; i++) {
var fieldRef = lunr.FieldRef.fromString(fieldRefs[i]),
field = fieldRef.fieldName
documentsWithField[field] || (documentsWithField[field] = 0)
documentsWithField[field] += 1
accumulator[field] || (accumulator[field] = 0)
accumulator[field] += this.fieldLengths[fieldRef]
}
for (var i = 0; i < this._fields.length; i++) {
var field = this._fields[i]
accumulator[field] = accumulator[field] / documentsWithField[field]
}
this.averageFieldLength = accumulator
}