Reshaping a table with date and characteristics in rows

Suppose I start with the table

date age18-24 age 25-34
1/1/2021 10 10
1/2/2021 20 30

Then want to generate a table

group date visitor

age 18-24 1/1/2021 10

age 18-24 1/2/2021 20

age 25-34 1/1/2021 10

age 25-34 1/2/2021 30

A brute force would be to vertically concatenate the tables and remove redundant columns. What function or procedures shall one use?

Answer 1

[Cris LaPierre]

See this answer

[alpedhuez]

Thank you.