Change multiple dataframes in a loop

Question

I have, for example, this three datasets (in my case, they are many more and with a lot of variables): ``` data_frame1 <- data.frame(a=c(1,5,3,3,2), b=c(3,6,1,5,5), c=c(4,4,1,9,2)) data_frame2 <- data.frame(a=c(6,0,9,1,2), b=c(2,7,2,2,1), c=c(8,4,1,9,2)) data_frame2 <- data.frame(a=c(0,0,1,5,1), b=c(4,1,9,2,3), c=c(2,9,7,1,1)) ``` on each data frame I want to add a variable resulting from a transformation of an existing variable on that data frame. I would to do this by a loop. For example: ``` datasets <- c("data_frame1","data_frame2","data_frame3") vars <- c("a","b","c") for (i in datasets){ for (j in vars){ # here I need a code that create a new variable with transformed values # I thought this would work, but it didn't... get(i)$new_var <- log(get(i)[,j]) } } ``` Do you have some valid suggestions about that? Moreover, it would be great for me if it were possible also to assign the new column names (in this case `new_var`) by a character string, so I could create the new variables…

Accepted Answer

You can put your dataframes in a list and use `lapply` to process them one by one. So no need to use a loop in this case.

For example you can do this :

```
data_frame1 <- data.frame(a=c(1,5,3,3,2), b=c(3,6,1,5,5), c=c(4,4,1,9,2))
data_frame2 <- data.frame(a=c(6,0,9,1,2), b=c(2,7,2,2,1), c=c(8,4,1,9,2))
data_frame3 <- data.frame(a=c(0,0,1,5,1), b=c(4,1,9,2,3), c=c(2,9,7,1,1))

ll <- list(data_frame1,data_frame2,data_frame3)
lapply(ll,function(df){
  df$log_a <- log(df$a)          ## new column with the log a
  df$tans_col <- df$a+df$b+df$c  ## new column with sums of some columns or any other           
                                 ##   transformation
  ###  .....
  df

})
```

the dataframe1 becomes :

```
[[1]]
  a b c     log_a tans_col
1 1 3 4 0.0000000        8
2 5 6 4 1.6094379       15
3 3 1 1 1.0986123        5
4 3 5 9 1.0986123       17
5 2 5 2 0.6931472        9
```

Change multiple dataframes in a loop

Solution

Problem