Dr. Joan Tan - with vs within

with evaluates an expression in an environment constructed from data, possibly modifying the data in the process. within is similar to with, except that it modifies the data frame directly and only examines the environemnt after the evaluation of the expression.

Case study 1: to create a new variable new_var in df that is the sum of var1 and var2

df <- data.frame(var1 = 1:10, var2 = 11:20)
df

   var1 var2
1     1   11
2     2   12
3     3   13
4     4   14
5     5   15
6     6   16
7     7   17
8     8   18
9     9   19
10   10   20

# Method 1: with
df$new_var <- with(df, var1 + var2) 
# is equivalent to
df$new_var <- df$var1 + df$var2

df

   var1 var2 new_var
1     1   11      12
2     2   12      14
3     3   13      16
4     4   14      18
5     5   15      20
6     6   16      22
7     7   17      24
8     8   18      26
9     9   19      28
10   10   20      30

# Method 2: within
within(df, new_var <- var1 + var2)

   var1 var2 new_var
1     1   11      12
2     2   12      14
3     3   13      16
4     4   14      18
5     5   15      20
6     6   16      22
7     7   17      24
8     8   18      26
9     9   19      28
10   10   20      30

# Method 3: mutate
library(dplyr)
df %>% mutate(new_var = var1 + var2)

   var1 var2 new_var
1     1   11      12
2     2   12      14
3     3   13      16
4     4   14      18
5     5   15      20
6     6   16      22
7     7   17      24
8     8   18      26
9     9   19      28
10   10   20      30

Case study 2: to create a new variable new_var in df that is the sum of var1 and var2; new_var2 is the product of var1 and var3.

df <- data.frame(var1 = 1:10, var2 = 11:20, var3 = 21:30)
within(df, {
  new_var <- var1 + var2
  new_var2 <- var1 * var3
})

   var1 var2 var3 new_var2 new_var
1     1   11   21       21      12
2     2   12   22       44      14
3     3   13   23       69      16
4     4   14   24       96      18
5     5   15   25      125      20
6     6   16   26      156      22
7     7   17   27      189      24
8     8   18   28      224      26
9     9   19   29      261      28
10   10   20   30      300      30

df

   var1 var2 var3
1     1   11   21
2     2   12   22
3     3   13   23
4     4   14   24
5     5   15   25
6     6   16   26
7     7   17   27
8     8   18   28
9     9   19   29
10   10   20   30

In the code chunk above, two new columns are being created and please note that no column has been added to the original data. You have to assign the output from the within environment to a new object.

Citation

BibTeX citation:

@online{tan2024,
  author = {Tan, Joan},
  title = {`With` Vs `Within`},
  date = {2024-01-16},
  url = {https://joantan.org/R/2024-01-16-with-within/},
  langid = {en}
}

For attribution, please cite this work as:

Tan, Joan. 2024. “`With` Vs `Within` .” January 16, 2024. https://joantan.org/R/2024-01-16-with-within/.