Replace any values in a data frame based on another data frame

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Here is one way:

# you have to be careful about mucking with factors
# convert columns to factors after you have finished
# changing values in them
# start by not creating factors in the first place
df1 <- data.frame( col1 = 1:6
                  , col2 = c( rep( "a", 3 )
                            , rep( "b", 3 )
                            )
                  , col3 = c( rep( "AA", 2 )
                            , rep( "BB", 2 )
                            , rep( "CC", 2 )
                            )
                  , col4 = c( 1, 8, 6, 9, 7, 6 )
                  , stringsAsFactors = FALSE
                  )

df2 <- data.frame( col1 = c( 1, 3, 5, 6 )
                  , col2 = c( rep( "a", 2 )
                            , rep( "b", 2 )
                            )
                  , col3 = c( rep( "AA", 1 )
                            , rep( "EE", 1 )
                            , rep( "FF", 1 )
                            , rep( "CC", 1 )
                            )
                  , col4 = c( 1, 8, 5, 9 )
                  , stringsAsFactors = FALSE
                  )

df3 <- merge( df1, df2, by = c( "col1", "col2" ), all = TRUE )
idx <- !is.na( df3$col3.y )
df3$col3.x[ idx ] <- df3$col3.y[ idx ]
df3$col4.x[ idx ] <- df3$col4.y[ idx ]
df3$col3.y <- df3$col4.y <- NULL
names( df3 )[ 3:4 ] <- c( "col3", "col4" )
df3

Hello,

I have two data frames with different sizes but with the same number of columns.

df1 <- data.frame(col1 = c(1:6), col2 = c(rep("a", 3), rep("b", 3)), col3 = c(rep("AA", 2), rep("BB", 2), rep("CC", 2)), col4=c(1,8,6,9,7,6))

df1

 col1 col2 col3 col4

1    1    a   AA    1

2    2    a   AA    8

3    3    a   BB    6

4    4    b   BB    9

5    5    b   CC    7

6    6    b   CC    6

df2< - data.frame(col1 = c(1,3,5,6), col2 = c(rep("a", 2), rep("b", 2)), col3 = c(rep("AA", 1), rep("EE", 1), rep("FF", 1), rep("CC", 1)), col4=c(1,8,5,9))

df2

 col1 col2 col3 col4

1    1    a   AA    1

2    3    a   EE    8

3    5    b   FF    5

4    6    b   CC    9





Based on col1 and col2, how can I replace any values in col3 and col4 of df1 which don't match with those of df2 by the values of df2



In this example, the result will be:

df1

  col1 col2 col3 col4

1    1    a   AA    1

2    2    a   AA    8

3    3    a   EE    8

4    4    b   BB    9

5    5    b   FF    5

6    6    b   CC    9



Thanks a lot for your help.

Have a nice day

Marine

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