CODEWITHSUNDEEP
r
sgp667
sgp667

Reputation: 1875

Getting mean of a subset within data.frame

I have a data frame that displays sales data, split by Year, and Quarter. What I want to do is plot Demand with respect to Price, however I'd like to see price as difference from average annual price.

What I have thus far is 

Year <- c(1,1,1,2,2,2,2)
Quarter <- c(1,2,3,4,1,2,3,4)
Price <- c(10,15,20,15,15,20,20,25)
Demand <- c(12,15,10,12,10,15,12,12)
sales_data <- data.frame(Year, Quarter, Price, Demand)
attach(sales_data)    
plot(Price-mean(Price),Demand)
#Correct prices:
#year1 -5,0,5,0
#year2 -5,0,0,5

Of course the issue with this is that mean() uses all of data not just data from each year separately.

Upvotes: 0

Views: 48

Answers (1)

chinsoon12
chinsoon12

Reputation: 25225

using base by function

plot(unlist(by(sales_data, sales_data$Year, function(x) x$Price - mean(x$Price))),Demand)

Upvotes: 1

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