R- Referencing different dataframes in a loop - r

Question

I am brand new to R so if I'm thinking about this completely wrong feel free to tell me. I have a series of imported dataframes on power plants, one of each year (Plant1987, Plant1988 etc...) that I am trying to combine ultimately into one data frame. Prior to doing so, I'd like to add a "year" variable to each dataframe. I could do this for each individual dataframe, but would like to formalize it and do it in one step. I know how to do it in stata, but I'm struggling here.
I was thinking something along the lines of:
for (y in 1987:2008) {
paste("Plant",y,sep="")$year <- y
}
which doesn't work because paste is obviously not the right function. Is there a smart, quick way to do this? Thanks

Answer 1

Try this ..
year=seq(1987,2008,by=1)
list_object_names = sprintf("Plant%s", 1987:2008)
list_DataFrame = lapply(list_object_names, get)
for (i in 1:length(list_DataFrame ) ){
list_DataFrame[[i]][,'Year']=year[i]
}

Answer 2

Here are some codes to give you some ideas. I used the mtcars data frame as an example to create a list with three data frames. After that I used two solutions to add the year (2000 to 2002) to each data frame. You will need to modify the codes for your data.
# Load the mtcars data frame
data(mtcars)
# Create a list with three data frames
ex_list <- list(mtcars, mtcars, mtcars)
# Create a list with three years: 2000 to 2002
year_list <- 2000:2002
Solution 1: Use lapply from base R
ex_list2 <- lapply(1:3, function(i) {
dt <- ex_list[[i]]
dt[["Year"]] <- year_list[[i]]
return(dt)
})
Solution 2: Use map2 from purrr
library(purrr)
ex_list3 <- map2(ex_list, year_list, .f = function(dt, year){
dt$Year <- year
return(dt)
})
ex_list2 and ex_list3 are the final output.

Answer 3

Let's say you have data.frames
Plant1987 <- data.frame(plantID=1:4, x=rnorm(4))
Plant1988 <- data.frame(plantID=1:4, x=rnorm(4))
Plant1989 <- data.frame(plantID=1:4, x=rnorm(4))
You could put a $year column in each with
year <- 1987:1989
for(yeari in year) {
eval(parse(text=paste0("Plant",yeari,"$year<-",yeari)))
}
Plant1987
# plantID x year
# 1 1 0.67724230 1987
# 2 2 -1.74773250 1987
# 3 3 0.67982621 1987
# 4 4 0.04731677 1987
# ...etc for other years...
...and either bind them together into one data.frame with
df <- Plant1987
for(yeari in year[-1]) {
df <- rbind(df, eval(parse(text=paste0("Plant",yeari))))
}
df
# plantID x year
# 1 1 0.677242300 1987
# 2 2 -1.747732498 1987
# 3 3 0.679826213 1987
# 4 4 0.047316768 1987
# 5 1 1.043299473 1988
# 6 2 0.003758675 1988
# 7 3 0.601255190 1988
# 8 4 0.904374498 1988
# 9 1 0.082030356 1989
# 10 2 -1.409670456 1989
# 11 3 -0.064881722 1989
# 12 4 1.312507736 1989
...or in a list as
itsalist <- list()
for(yeari in year) {
eval(parse(text=paste0("itsalist$Plant",yeari,"<-Plant",yeari)))
}
itsalist
# $Plant1987
# plantID x year
# 1 1 0.67724230 1987
# 2 2 -1.74773250 1987
# 3 3 0.67982621 1987
# 4 4 0.04731677 1987
#
# $Plant1988
# plantID x year
# 1 1 1.043299473 1988
# 2 2 0.003758675 1988
# 3 3 0.601255190 1988
# 4 4 0.904374498 1988
#
# $Plant1989
# plantID x year
# 1 1 0.08203036 1989
# 2 2 -1.40967046 1989
# 3 3 -0.06488172 1989
# 4 4 1.31250774 1989