How to combine two dataframe value in R

Question

I want to create one dataframe(result df) from two dataframes(df1, df2).

How do I make the 'result df' below?

df1 <- data.frame('user'=c('user1', 'user2', 'user3'),
              'item1'=c(10,5,1),
              'item2'=c(5,3,8),
              'item3'=c(1,7,10))

df2 <- data.frame('user'=c('user1', 'user2', 'user3'),
              'ratio'=c(0.5,0.3,0.2))

Answer 1

Try the code below

> colSums(df1[-1]*df2$ratio)
item1 item2 item3 
  6.7   5.0   4.6

Answer 2

You need to convert your data frames into matrices

df1 <- data.frame('user'=c('user1', 'user2', 'user3'),
                  'item1'=c(10,5,1),
                  'item2'=c(5,3,7),
                  'item3'=c(1,8,10))

df2 <- data.frame('user'=c('user1', 'user2', 'user3'),
                  'ratio'=c(0.5,0.3,0.2))


res <- as.numeric(as.matrix(df1[,-1])%*%as.matrix(df2[,2]))

names(res) <- c("item1","item2", "item3")

#Output
res
item1 item2 item3 
  6.7   5.0   4.6