Lint repeated if/else if/ else after a certain threshold?

[IndrajeetPatil]

After a certain point, a block of conditional statements can become quite difficult to read, maintain, and extend further.

To see what I mean, consider this example from {insight}:

if (transform_fun == "identity") {
  out <- list(transformation = function(x) x, inverse = function(x) x)
} else if (transform_fun == "log") {
  out <- list(transformation = log, inverse = exp)
} else if (transform_fun %in% c("log1p", "log(x+1)")) {
  out <- list(transformation = log1p, inverse = expm1)
} else if (transform_fun == "log10") {
  out <- list(transformation = log10, inverse = function(x) NA)
} else if (transform_fun == "log2") {
  out <- list(transformation = log2, inverse = function(x) NA)
} else if (transform_fun == "exp") {
  out <- list(transformation = exp, inverse = log)
} else if (transform_fun == "sqrt") {
  out <- list(transformation = sqrt, inverse = function(x) x^2)
} else if (transform_fun == "power") {
  out <- list(transformation = function(x) x^2, inverse = sqrt)
} else if (transform_fun == "expm1") {
  out <- list(transformation = expm1, inverse = log1p)
} else if (transform_fun == "log-log") {
  out <- list(
    transformation = function(x) log(log(x)),
    inverse = function(x) exp(exp(x))
  )
}

The alternative here is to create a look-up table (using a data frame, named vector/list, etc.), which is much easier to read, and importantly, extend - we just need to add another row for every new transformation:

df <- tibble::tribble(
  ~transform_fun, ~out,
  "identity",     list(transformation = function(x) x, inverse = function(x) x),
  "log",          list(transformation = log, inverse = exp),
  "log1p",        list(transformation = log1p, inverse = expm1),
  "log(x+1)",     list(transformation = log1p, inverse = expm1),
  "log10",        list(transformation = log10, inverse = function(x) NA),
  "log2",         list(transformation = log2, inverse = function(x) NA),
  "exp",          list(transformation = exp, inverse = log),
  "sqrt",         list(transformation = sqrt, inverse = function(x) x^2),
  "power",        list(transformation = function(x) x^2, inverse = sqrt),
  "expm1",        list(transformation = expm1, inverse = log1p),
  "log-log",      list(transformation = function(x) log(log(x)), inverse = function(x) exp(exp(x)))
)

---

That said, I am not sure where to draw the line, i.e., how many repeats of if + else if is too many. Maybe this can be configurable?

Also, note that this is a different linter from any of the existing or proposed ones:

• nested ifelse()
• redundant ifelse()
• deeply nested conditionals (Introduce linter for deeply nested code? #1848)

That said, IINM, it does have some overlap with Google's IfSwitchLinter().

[MichaelChirico]

yes, this is basically the IfSwitchLinter. We have not deployed that in the end internally -- it needs some fine-tuning.

I think the key is the cyclomatic complexity of the internal expressions. when each branch is complex, branching actually helps readability we found.

[MichaelChirico]

Related thing I've been meaning to write some linting for eventually (not sure if it can be subsumed here too):

if (x == "a") {
  # code that doesn't overwrite x
}
if (x == "b") {
  # code that doesn't overwrite x
}

can be collapsed to an if/else. the part where we also have to test if the condition variable is changing makes it tough.

[MichaelChirico]

See #2304 for the initial implementation of a related linter.

[IndrajeetPatil]

Closed by #2304