how can i make a histogram for date?

i have a netcdf file as below:

Format:

           classic
Dimensions:
           altitude = 150
           index    = 30619
Variables:
    altitude    
           Size:       150x1
           Dimensions: altitude
           Datatype:   single
    occultation 
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    year and day
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    hour        
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    latitude    
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    longitude   
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    beta angle  
           Size:       30619x1
           Dimensions: index
           Datatype:   single
    N2O         
           Size:       150x30619
           Dimensions: altitude,index
           Datatype:   single
    N2O error   
           Size:       150x30619
           Dimensions: altitude,index
           Datatype:   single
    quality flag
           Size:       150x30619
           Dimensions: altitude,index
           Datatype:   single

now i want to make a histogram for date including year and month ( from year and day (30619x1)) and put N2O ( 150x30619) in to this histogram for different altitudes(150x1). the example of the format of date data is as below:

2004010

in which first 4 digit represents year and last 3 digit represents day.

thank you