从一个数据帧传输到另一个plyr

Question

我有一个数据帧，看起来像这样：

library(car) 
mtcarsSubset <- car::some(mtcars) 
mtcarsSubset <- mtcarsSubset[, c("mpg", "drat")] 
mtcarsSubset$rows <- rownames(mtcarsSubset) 

mtcarsSubset 
        mpg drat    rows 
Datsun 710   22.8 3.85   Datsun 710 
Duster 360   14.3 3.21   Duster 360 
Merc 240D   24.4 3.69   Merc 240D 
Merc 280   19.2 3.92   Merc 280 
Merc 450SLC  15.2 3.07  Merc 450SLC 
Cadillac Fleetwood 10.4 2.93 Cadillac Fleetwood 
Toyota Corolla  33.9 4.22  Toyota Corolla 
Toyota Corona  21.5 3.70  Toyota Corona 
Dodge Challenger 15.5 2.76 Dodge Challenger 
Ford Pantera L  15.8 4.22  Ford Pantera L 

我有一个看起来像这样的第二个数据帧：

mtcars <- mtcars[,c("gear", "carb")] 
mtcars$new.variable <- NA 
mtcars$rows <- rownames(mtcars) 
        gear carb new.variable    rows 
Mazda RX4    4 4   NA   Mazda RX4 
Mazda RX4 Wag   4 4   NA  Mazda RX4 Wag 
Datsun 710    4 1   NA   Datsun 710 
Hornet 4 Drive   3 1   NA  Hornet 4 Drive 
Hornet Sportabout  3 2   NA Hornet Sportabout 
Valiant    3 1   NA    Valiant 
Duster 360    3 4   NA   Duster 360 
Merc 240D    4 2   NA   Merc 240D 
Merc 230    4 2   NA   Merc 230 
Merc 280    4 4   NA   Merc 280 
Merc 280C    4 4   NA   Merc 280C 
Merc 450SE    3 3   NA   Merc 450SE 
Merc 450SL    3 3   NA   Merc 450SL 
Merc 450SLC   3 3   NA   Merc 450SLC 
Cadillac Fleetwood  3 4   NA Cadillac Fleetwood 
Lincoln Continental 3 4   NA Lincoln Continental 
Chrysler Imperial  3 4   NA Chrysler Imperial 
Fiat 128    4 1   NA   Fiat 128 
Honda Civic   4 2   NA   Honda Civic 
Toyota Corolla   4 1   NA  Toyota Corolla 
Toyota Corona   3 1   NA  Toyota Corona 
Dodge Challenger  3 2   NA Dodge Challenger 
AMC Javelin   3 2   NA   AMC Javelin 
Camaro Z28    3 4   NA   Camaro Z28 
Pontiac Firebird  3 2   NA Pontiac Firebird 
Fiat X1-9    4 1   NA   Fiat X1-9 
Porsche 914-2   5 2   NA  Porsche 914-2 
Lotus Europa   5 2   NA  Lotus Europa 
Ford Pantera L   5 4   NA  Ford Pantera L 
Ferrari Dino   5 6   NA  Ferrari Dino 
Maserati Bora   5 8   NA  Maserati Bora 
Volvo 142E    4 2   NA   Volvo 142E 

凡mtcarsSubset平等的rowrows的mtcars，我想转让mpg。我可以用这个实现这个for循环：

for (i in seq_along(mtcarsSubset$rows)) { 

    x <- which(mtcars$rows == mtcarsSubset$rows[i]) 
    mtcars$new.variable[x] <- mtcarsSubset$mpg[i] 

} 

        gear carb new.variable    rows 
Mazda RX4    4 4   NA   Mazda RX4 
Mazda RX4 Wag   4 4   21.0  Mazda RX4 Wag 
Datsun 710    4 1   22.8   Datsun 710 
Hornet 4 Drive   3 1   NA  Hornet 4 Drive 
Hornet Sportabout  3 2   NA Hornet Sportabout 
Valiant    3 1   18.1    Valiant 
Duster 360    3 4   NA   Duster 360 
Merc 240D    4 2   24.4   Merc 240D 
Merc 230    4 2   NA   Merc 230 
Merc 280    4 4   19.2   Merc 280 
Merc 280C    4 4   NA   Merc 280C 
Merc 450SE    3 3   NA   Merc 450SE 
Merc 450SL    3 3   NA   Merc 450SL 
Merc 450SLC   3 3   15.2   Merc 450SLC 
Cadillac Fleetwood  3 4   NA Cadillac Fleetwood 
Lincoln Continental 3 4   NA Lincoln Continental 
Chrysler Imperial  3 4   NA Chrysler Imperial 
Fiat 128    4 1   32.4   Fiat 128 
Honda Civic   4 2   NA   Honda Civic 
Toyota Corolla   4 1   NA  Toyota Corolla 
Toyota Corona   3 1   NA  Toyota Corona 
Dodge Challenger  3 2   NA Dodge Challenger 
AMC Javelin   3 2   15.2   AMC Javelin 
Camaro Z28    3 4   13.3   Camaro Z28 
Pontiac Firebird  3 2   NA Pontiac Firebird 
Fiat X1-9    4 1   27.3   Fiat X1-9 
Porsche 914-2   5 2   NA  Porsche 914-2 
Lotus Europa   5 2   NA  Lotus Europa 
Ford Pantera L   5 4   NA  Ford Pantera L 
Ferrari Dino   5 6   NA  Ferrari Dino 
Maserati Bora   5 8   NA  Maserati Bora 
Volvo 142E    4 2   NA   Volvo 142E 

我一个plyr的解决方案后，特别是要完成的mpg从mtcarsSubset转移到mtcars。我设想要么ddply()或ldply将能够实现这一点，虽然我不知道如何。这可能与plyr？

Answer 1

这里是一种方法，特别是与plyr结合ifelse()做到这一点。如果您使用ddply()和transform，则不需要初始化变量“new.variable”。

require(plyr)

ddply(mtcars, .(rows), transform, new.variable = ifelse(rows %in% mtcarsSubset$rows, mtcarsSubset$mpg[mtcarsSubset$rows == rows], NA))

Answer 2

也许您在寻找merge()？

merge(mtcars, mtcarsSubset[ , "new.variable"], by="row.names", all.x=T)