How to group numeric data into ranges in Rails -

in rails 3.2 app have following model

create_table "people", |t|   t.integer  "height" end 

the height attribute person's height in cm.

i want group data in table 5cm height classes, , return count each height class. e.g.,

{"height_classes":[150-155, 155-160, 160-165],"height_counts":[1, 3, 11]} 

how can group classes this?

so far i've used following:

step = 5 data = people.all.sort_by &:length height_classes = data.map{ |d| d.height - (d.length % step) }.uniq height_counts = height_classes.map{ |hc| data.select{ |d| d.length - (d.length % step) == l }.count} 

but not meeting needs. achieve is:

• the height_classes run minimum maximum values in height column (but adjusted 5cm class - i.e. if minimum value 172 grouping should 170-175)
• any empty classes should included, count of zero
• the height_classes should string displaying range of values

is possible?