27.16 Assignment

20200105

Avoid using base::= for assignment. It was introduced in S-Plus in the late 1990s as a convenience but is ambiguous (named arguments in functions, mathematical concept of equality). The traditional backward assignment operator base::<- implies a flow of data and for readability is explicit about the intention.

Preferred

a <- 42
b <- mean(x)

Discouraged

a = 42
b = mean(x)

The forward assignment base::-> should generally be avoided. A single use case justifies it in pipelines where logically we do an assignment at the end of a long sequence of operations. As a side effect operator it is vitally important to highlight the assigned variable whenever possible and so out-denting the variable after the forward assignment to highlight it is recommended.

Preferred

ds[vars] %>%
  sapply(function(x) all(x == x[1L])) %>%
  which() %>%
  names() %T>%
  print() ->
constants

Traditional

constants <-
  ds[vars] %>%
  sapply(function(x) all(x == x[1L])) %>%
  which() %>%
  names() %T>%
  print()

Discouraged

ds[vars] %>%
  sapply(function(x) all(x == x[1L])) %>%
  which() %>%
  names() %T>%
  print() ->
  constants

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