If we want to study or compare some issues that time we need classification as huge number of subjects (people) cannot be studied individually. For classification criteria differs from place to place. Like if we are studying a classroom there will be different criteria in compare to subjects of scientific research or other places. Wherever we are doing classification we have to consider variations.
School: Suppose we are studying in a school. It can be classified according to the gender - girls and boys. The students can be classified according to the standard of classes - 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc., or into two group of standard-juniors (1 - 5) and seniors (6 - 12). Even entire pupils of school can be divided into different age groups. May be age group A (3 - 5 yrs), age group B (6 - 9 yrs), age group C (10 - 12 yrs), age group D (13 - 15 yrs), age group E (16 - 17 yrs). According to height we can also classify students into several groups by above mentioned process.
Classrooms: If we consider single classroom, then it cannot be categorize according to age, height and standard. Because students of same classroom have same range of height, age and standard. So, in that case we can categorize students according to their gender (girls and boys), ranges of roll number, according to their gradation or alphabetical order of their name. If the names are same for more than one student then surname will be considered.
Canteen: People can be classified according to their food habit. People those who eat animal protein are non-vegetarian and those who don’t eat animal protein are called vegetarian.
Offices: People those who are working in an office can be categorize into – gender (male and female), different classes according to their classes of work-executive, workers, subordinates etc.
Scientific research: In science different people have taken different subject for research. In this case it can be categorize into several groups-
Age group can be classified as new born, child, adult, old people. This category is prepared according to different age group.
Disease affected: Suppose the research is for any drug testing. That time two category will be there. One is control (people without that particular disease) and patient (people having that disease).
Gender is classified as male and female.
Hospital: People of this subject can be categorize patient, doctors, nurse (by profession), according to the gender (male and female), different wards are there for different patient. Like cardiology (heart disease), ophthalmologist (eye disease), nephrologist (disease of kidney), psychiatrist (mental illness), orthopaedic (regarding bone) etc.
Family and neighbours: Last but not the least we met our family and neighbours mostly. We can categorize the member according to the gender – male (father, brother, grandfather, forefathers, uncle, husband, son, grandson etc.) and female (mother, sister, wife, grandmother, daughter, grand-daughter, etc,).
We can categorize them according to their age also- elder (greater than our age), younger (lesser than our age) and same age (same as our age).
Suppose you are playing in your school cricket team. How will you categorize your team mate?
I can categorize the team in two ways-
(a) Captain, vice captain and players. (according to their designation).
(b) Batsman, bowlers and all rounder.