R-在某些条件下比较矩阵中的行

Question

I have a history table (table: HT) containing purchase information in the following structure

Supplierno itemno price
ABC123 101 50
ABC124 105 55
BCD201 103 60
BCD211 103 60
EFG103 103 45

Then I get new data in the same format(table: NT) on a periodic basis. I want to determine cases in the new data feed, where vendors are supplying the same item at prices . I wanted to the equivalent of a SQL query that will do a

select NT.* from newtable where NNT.itemno=HT.itemno AND NT.price<>1.2*HT.price

I tried HT[HT[(HT.itemno==NT.itemno) & (HT.price!=NT.price)] but always get 0 results even though there are instances that should get picked up.

Somehow comparing columns in a row works well with this approach, but not same column across rows

I know I can run loops but my HT table is large(>1M) and understand thinking vectors will be more efficient.

Look forward for inputs and guidance

Answer 1

Using data.table you can also try: (reusing @Wave's example)

library(data.table)
HT=data.table(supplier=c("ABC123","ABC124","BCD201"),itemno=101:103,price=c(50,55,60))
NT=data.table(supplier=c("ABC123","ABC124","BCD201"),itemno=101:103,price=c(50,55,65))
merge(HT,NT,by=c("itemno","supplier"))[price.x!=price.y]

Answer 2

To recreate you data:

HT=data.frame(supplier=c("ABC123","ABC124","BCD201"),itemno=101:103,price=c(50,55,60))

NT=data.frame(supplier=c("ABC123","ABC124","BCD201"),itemno=101:103,price=c(50,55,65))

To select from the new dataframe the cases where the price is changed:

NT[NT$itemno %in% HT$itemno & NT$price!=HT$price,]