I give a simplified example in order to more clearly explain the situation.
Example: in store "A" (file A) there are 1000 watermelons, each with its own price and weight. To compile a linear regression equation, we need the result of the function lm.
In this case, we use:
a <- lm (data = A, formula = price ~ wigth) then summary (a) and voila ...
But not everything is so simple) Watermelons still have an example for an example - the country where they were grown ("Turkey" and "Spain"). So I understand that the question is very simple, but I have already raised my mind to seek a solution. How can I write a linear regression equation using the lm function only for watermelons from Turkey or only Spain. Rather, where and how to include this parameter in a <-lm (data = 'A', formula = price ~ wigth ???????)
