如何使用已编写的 for 循环创建函数以在 r 环境中自动创建向量

Question

I have a df with fixed columns and unfixed row number. I created empty vectors and populate R commands to create vectors on its own once I use eval(parse(text = someVector)) . What I did with for-loop works, but I would like to turn it into a function and/or use *apply() and I don't know how to do that. I would very much like to upgrade my programming skills. I would like to be able to choose the variables by name or position and always go through every row.

working with the reprex, I expect 30 vectors created in the working environment - for every car model for the specified column separate vector to store the value of that column for this row/carmodel and 6 more vectors that store the R commands.

for example one of the vectors should look like this: cyl_MazdaRX4Wag <- 6

# df
df <- mtcars[1:5,]  
df$carmodel <- gsub("[[:space:]]", "", rownames(df))


# create empty vectors to store R command 
carmodel <- c() 
mpg <- c() 
cyl <- c() 
hp <- c() 
gear <- c() 
carb <- c()

# loop through every row to create an R command
for(i in 1:nrow(df)){
     carmodel[i] <-  paste0("carmodel_", df$carmodel[i] , " <- ", "'", df$carmodel[i], "'",";")
     mpg[i] <-  paste0("mpg_", df$carmodel[i],  " <- ", df$mpg[i], ";")   
     cyl[i] <-  paste0("cyl_", df$carmodel[i],  " <- ", df$cyl[i], ";")   
     hp[i] <-  paste0("hp_", df$carmodel[i],  " <- ", df$hp[i], ";") 
     gear[i] <-  paste0("gear_", df$carmodel[i],  " <- ", df$gear[i], ";")  
     carb[i] <-  paste0("carb_", df$carmodel[i],  " <- ", df$carb[i], ";")  
}
# collapse the vectors in one string
carmodel <- paste(carmodel, collapse = " ") 
mpg <- paste(mpg, collapse = " ")
cyl <- paste(cyl, collapse = " ")
hp <- paste(hp, collapse = " ") 
gear <- paste(gear, collapse = " ") 
carb <- paste(carb, collapse = " ")

# execute R command
eval(parse(text = carmodel)) 
eval(parse(text = mpg)) 
eval(parse(text = cyl)) 
eval(parse(text = hp)) 

# delete vectors that store the R commands
rm(list = c("carmodel","mpg","cyl", "hp","gear","carb"))
eval(parse(text = gear)) 
eval(parse(text = carb))

Answer 1

We can select columns on which we want to work. Create a named vector with name and it's value.

cols <- c('carmodel', 'mpg', 'cyl', 'hp', 'gear', 'carb')
temp <- unlist(lapply(cols, function(x) as.list(setNames(df[[x]], 
                           paste0(x, df$carmodel)))), recursive = FALSE)

Usually, it is better to keep data as a list, rather than individual objects. If you need them as separate variables in the global environment we can use list2env .

list2env(temp, .GlobalEnv)