在R中使用带有三个数据帧的多个循环

Question

我有3个数据框并尝试遍历每个类别以获得每周的总（总和）交易数据$金额。

这是我的伪代码：

for a given productIDCat$Category {
           for a given weeklydate$weekid{
                     calculate sum(transactiondata$amount)
                     when transactiondata$date is between weeklydate$begindate
                     and weeklydate$enddate 
                     Append sum to new column in weeklydate
                     as weeklydate$testamount}}

Repeat this process for each week for that given product.

以下是我的数据框：

productIDCat

itemNo  Category
  1  Shoes
  2  Shirts
  3  Panties
  4  Shoes
  5  Shirts
  6  Panties

transactiondata

amount  date itemNo
      12  2014-07-23 1
      33  2014-07-29 1
      6  2014-08-05 2
      21  2014-08-06 2
      23  2014-08-19 3
      32  2014-08-27 3

weeklydate

weekid  begindate enddate
      1  2014-07-21 2014-07-25
      2  2014-07-28 2014-08-01
      3  2014-08-04 2014-08-08
      4  2014-08-11 2014-08-15
      5  2014-08-18 2014-08-22
      6  2014-08-25 2014-08-29