Match row names and column names to values in another data frame

Question

I have two data frames as follows :

df1 <- t(data.frame(seq(1,6,by=1),seq(6,1,by=-1)))    
colnames(df1) <- c("A","B","C","D","E","F)    
rownames(df1) <- c("a","b")    
df2 <- data.frame(rep(colnames(df1),2),rep(rownames(df1),6))    
colnames(df2) <- c("Vector1","Vector2")

Such that

df1

     A   B   C   D   E   F
  a  1   2   3   4   5   6
  b  6   5   4   3   2   1

df2

   Vector1    Vector2
     A           a
     B           b
     C           a
     D           b
     E           a
     F           b
     A           a
     B           b
     C           a
     D           b
     E           a
     F           b

I want to match the column values of df2 to column names and row names of df1, and fill the corresponding value to a new column in df2 as follows:

 Vector1 Vector2   Newcol
   A       a         1
   B       b         5
   C       a         3
   D       b         3
   E       a         5
   F       b         1
   A       a         1
   B       b         5
   C       a         3
   D       b         3
   E       a         5
   F       b         1

Any suggestions would be much appreciated. Thanks.

Answer 1

We can use merge with melt . The melt returns a three column data.frame , merge it with the second dataset to create the new column

library(reshape2)
merge(df2, melt(df1), by.x = c("Vector1", "Vector2"), by.y = c("Var2", "Var1"))

---

Or a base R option would be to get the numeric index with match after paste ing the 'df2' rowwise ( do.call(paste ) and get the paste d column names and row names of 'df1' using outer . Using the numeric index, we get the values in 'df1' to create the 'Newcol'

df2$Newcol <- df1[match(do.call(paste, df2), 
                       t(outer(colnames(df1), rownames(df1), FUN = paste)))]
df2$Newcol
#[1] 1 5 3 3 5 1 1 5 3 3 5 1