Aggregating Data in R Data Frame

Question

I have a csv file similar to below:

Name - Year - Genre - Sales

1 - 2005 - Action - 1

2 - 2005 - Action - 2

3 - 2005 - Shooter - 3

4 - 2006 - RPG - 2

5 - 2006 - RPG - 2

6 - 2007 - Action - 1

7 - 2007 - Shooter - 3

8 - 2007 - RPG - 2

...

My end goal is to make a sand chart in R that shows the total sales of each genre on the y axis and year on the x axis, with the labels being the genres.

I need to sum up the sales of each of the genres per year, for example 2005 sales would be Action:3, Shooter:3, RPG:0. And do this for every year.

This would eventually give me a data frame that looks like this:

 Action  Shooter  RPG  

2005 3 3 0

2006 0 0 4

2007 1 3 2

In Python, I could do this using enumerate, but I'm having a hard time figuring this out in R.

Here's what I have so far

vg <- read.csv("vgdata.csv")

genres <- unique(vg$Genre)
years <- sort(unique(vg$Year))

genredf <-data.frame(vg$Genre)
i<-0
for (year in (unique(vg$Year))) {
  yeardata = rep(0,length(genres))
}

This would give me the data frame with 0s in it. Now I'm trying to add in the summation of the data so I can chart it.

Sorry for the poor formatting. I'm still new to stack overflow.

Answer 1

We could use xtabs

xtabs(Sales ~ Year + Genre, df1)

Answer 2

Here is a base R solution using reshape + aggregate (but seems not as simple as the approach of xtabs @akrun )

dfout <- reshape(aggregate(Sales~Year + Genre,df,sum),
                 direction = "wide",
                 idvar = "Year",
                 timevar = "Genre")

such that

> dfout
  Year Sales.Action Sales.RPG Sales.Shooter
1 2005            3        NA             3
2 2007            1         2             3
3 2006           NA         4            NA

DATA

df <- structure(list(Name = 1:8, Year = c(2005L, 2005L, 2005L, 2006L, 
2006L, 2007L, 2007L, 2007L), Genre = c("Action", "Action", "Shooter", 
"RPG", "RPG", "Action", "Shooter", "RPG"), Sales = c(1L, 2L, 
3L, 2L, 2L, 1L, 3L, 2L)), class = "data.frame", row.names = c(NA, 
-8L))