Multiplying columns from different dataframes with different lengths and two conditions in R

Question

I have two data frames with different lengths. I want to mutate the columns in data frame df with the multiplication of CAP * currency and Go * currency from df_cur . This should be done with the conditions that country and Year must be the same for the two data fames respectively. More specifically,

#df#

Country	Sector	Year	Cap	Go	Exposion
AUS	A	2000	100	200	0.2
AUS	B	2000	150	200	0.3
AUS	C	2000	160	160	0.25
AUS	A	2001	110	200	0.25
AUS	B	2001	140	190	0.4
AUS	C	2001	165	155	0.2
BEL	A	2000	50	150	0.1
BEL	B	2000	70	160	0.15
BEL	C	2000	100	200	0.2
BEL	A	2001	55	160	0.15
BEL	B	2001	65	140	0.1
BEL	C	2001	110	190	0.3

#df_cur#

country	year	currency
AUS	2000	0.58
AUS	2001	0.60
BEL	2000	0.92
BEL	2001	0.95

So, I want to transform df like:

#df#

Country	Sector	Year	Cap	Go	Exposion
AUS	A	2000	100*0.58	200*0.58	0.2
AUS	B	2000	150*0.58	300*0.58	0.3
AUS	C	2000	160*0.58	160*0.58	0.25
AUS	A	2001	110*0.6	200*0.6	0.25
AUS	B	2001	140*0.6	190*0.6	0.4
AUS	C	2001	165*0.6	155*0.6	0.2
BEL	A	2000	50*0.92	150*0.92	0.1
BEL	B	2000	70*0.92	160*0.92	0.15
BEL	C	2000	100*0.92	200*0.92	0.2
BEL	A	2001	55*0.95	160*0.95	0.15
BEL	B	2001	65*0.95	140*0.95	0.1
BEL	C	2001	110*0.95	190*0.95	0.3

I reviewed many answers from Multiplying columns of different size of 2 data frames but nothing worked for me.

My code sample:

Country<-c("AUS","AUS","AUS","AUS","AUS","AUS", "BEL", "BEL", "BEL", "BEL", "BEL", "BEL")
Sector<-c("A","B","C","A","B","C","A","B","C","A","B","C")
Year<-c("2000", "2000", "2000", "2001", "2001", "2001", "2000", "2000", "2000", "2001", "2001", "2001")
Cap<-c(100,150,160,110,140,165,50,70,100,55,65,110)
Go<-c(200,200,160,200,190,155,150,160,200,160,140,190)
Exposion<-c(0.2,0.3,0.25,0.25,0.4,0.2,0.1,0.15,0.2,0.15,0.1,0.3)
df<-data.frame(Country,Sector,Year,Cap,Go,Exposion)

country<-c("AUS","AUS", "BEL", "BEL")
Year<-c("200","2001","2000","2001")
currency<-c(0.58, 0.6, 0.92, 0.95)
df_cur<-data.frame(country,Year,currency)

Thank you very much for your time!

Answer 1

Welcome Panagiotis. The easiest is to first combine the two data.frames. Then in the second step you can create new columns with mutate() :

library(dplyr)

df %>%
  left_join(., df_cur) %>%
  mutate(cap2 = Cap * currency) %>%
  mutate(go2 = Go * currency)

Answer 2

Using data.table

library(data.table)
setDT(df)[df_cur, c("Cap", "Go") := 
     .(Cap * currency, Go * currency), on = .(Country = country, Year)]

-output

df
#    Country Sector Year    Cap    Go Exposion
# 1:     AUS      A 2000 100.00 200.0     0.20
# 2:     AUS      B 2000 150.00 200.0     0.30
# 3:     AUS      C 2000 160.00 160.0     0.25
# 4:     AUS      A 2001  66.00 120.0     0.25
# 5:     AUS      B 2001  84.00 114.0     0.40
# 6:     AUS      C 2001  99.00  93.0     0.20
# 7:     BEL      A 2000  46.00 138.0     0.10
# 8:     BEL      B 2000  64.40 147.2     0.15
# 9:     BEL      C 2000  92.00 184.0     0.20
#10:     BEL      A 2001  52.25 152.0     0.15
#11:     BEL      B 2001  61.75 133.0     0.10
#12:     BEL      C 2001 104.50 180.5     0.30