R: switch statement

First argument: numbers vs character

The behaviour of switch(…) depends on the type of its first argument.

If the first argument's type is a character string, the value of the argument is searched as name in the subsequent arguemnts. The value of the subsequent arguments that matches is returned:

txt <- 'three';

num <- switch(txt,
   'one'   = 1,
   'two'   = 2,
   'three' = 3,
   'four'  = 4,
   'five'  = 5
);

print(paste(txt, '=', num)); # three = 3

Github repository about-r, path: /statements/switch/match.R

In the other cases, the value of the first argument is coerced into an integer. The element that matches tne value of the integer is then returned:

num <- 4;

txt <- switch(num,
  'one'  ,
  'two'  ,
  'three',
  'four' ,
  'five'
);

print(paste(num, '=', txt)); # 4 = four

Github repository about-r, path: /statements/switch/index.R

Evaluating expressions

op    <- 'times';
val_1 <- 12 ;
val_2 <-  3 ;

switch (op,
  plus       = { res <- val_1 + val_2; },
  times      = { res <- val_1 * val_2; },
  minus      = { res <- val_1 - val_2; },
  divided_by = { res <- val_1 / val_2; }
);

cat(paste(val_1, op, val_2, '=', res, "\n"));
#
#  12 times 3 = 36

Github repository about-r, path: /statements/switch/expression.R

Switching on a range

In order to test for a range, the switch statement can be combined with the findInterval() function:

opinion <- 7;

txt <- switch(
          findInterval(
              opinion, c(
                1, 2.5,
                   4.5,
                   6.5,
                   8.5,
                  10.5)
         ),
         'Strongly disagree',
         'Disagree'         ,
         'Neutral'          ,
         'Agree'            ,
         'Strongly agree'
);

print(paste(opinion, 'corresponds to', txt));
#
#  7 corresponds to Agree

Github repository about-r, path: /statements/switch/range.R

See also the dplyr function case_when.