[R] Simple vector question.

[rkevinburton at charter.net]

I have some data that I read in via read.csv:

 sales2007 <- read.csv("Total2007.dat", header=TRUE)

The data looks like:

> sales2007[1:605,]
  Year DayOfYear    Sku Quantity CatId           Category       SubCategory
1 2007         1 100091        1 10862            HOLIDAY         Christmas
2 2007         1 100138        1 11160       PET COSTUMES Famous (Licensed)
3 2007         1 100194        1 10749 HATS, WIGS & MASKS    Wigs - Women's
4 2007         1 100432        1 10865            HOLIDAY            Easter
5 2007         1 100911        1 10120                MEN   Superheroes Men
. . . .
600 2007         2 139002        1 10413     GIRLS Historical Girls
601 2007         2 138959        1 10322      BOYS TV & Movies Boys
602 2007         2 139005        1 10334      BOYS    Toddlers Boys
603 2007         2 139052        1 10517      PLUS         Plus Men
604 2007         2 138906        1 10322      BOYS TV & Movies Boys
605 2007         2 138860        1     0 (Unknown)        (Unknown)
> 

The DayOfYear goes from 1:365. I would like to form a vector from this data where the length of the vector is 365 and the value at each index coeresponds to the sum of the Quantity column where DayOfYear equals the index. For example if I was to use just the sample above this new vactor call it 'DayOfYearSales' would be:
     DayOfYearSales[1] = 5
     DayOfYearSales[2] = 6
Since in the snippet above only DayOfYear = 1:2  is shown. I want to continue the sum for the whole data frame. I am sure this is fairly easy. I just cannot find out how to do it. Once I figure this out it would be relatively straightforward to apply the same principle to columns of like Category, SKU, or SubCategory.

Something like:

table(Category)

would give me the number of entires for each unique value but I want the Quantity column used in this tabulation kind of like a frequency.

Thank you.

Kevin