[R] merge dataframes with conditions formulated as logical expressions

[Wolfram Fischer]

I have a data.frame df containing two variables:
    GRP: Factor
    VAL: num

I have a data.frame dp containing:
    GRP: Factor
    MIN.VAL: num
    MAX.VAL: num
    VAL2: num
with several rows per "GRP"
where dp[i-1, "MAX.VAL"] < dp[i, "MIN.VAL"]
within the same "GRP".

I want to create df[i, "VAL2"] <- dpp[z, "VAL2"] 
with    i along df 
and     dpp <- subset( dp, GRP = df[i, "GRP"] )
so that it is true for each i:
        df[i, "VAL"] > dpp[z, "MIN.VAL"]
   and  df[i, "VAL"] <= dpp[z, "MAX.VAL"]

Is there an easy/efficient way to do that?

Example:
df <- data.frame( GRP=c( "A", "A", "B" ), VAL=c( 10, 100, 200 ) )
dp <- data.frame( GRP=c( "A", "A", "B", "B" ),
    MIN.VAL=c( 1, 50, 1, 70 ), MAX.VAL=c( 49, 999, 59, 999 ), 
    VAL2=c( 1.1, 2.2, 3.3, 4.4 ) )

The result should be:
    df$VAL2 <- c( 1.1, 2.2, 4.4 )

Thanks - Wolfram