3.3 Assignment

20220523 The assignment operator in R r Rfunction('<-',show.paren=FALSE) is used to save a result into the computer’s memory and give it a name that we can refer to later. We can use this operator to save the result of the sequence of operations from a pipeline (see Section 3.8).

# Select variables/observations and save the result.

rainy_days <-
  ds %>% 
  select(min_temp, max_temp, rainfall, sunshine) %>%
  filter(rainfall >= 1)

Within the pipe paradigm we can use the forward assignment operator base::-> to save the resulting data into a variable in a logically forward flowing way.

# Demonstrate use of the forward assignment operator.

ds %>% 
  select(min_temp, max_temp, rainfall, sunshine) %>%
  filter(rainfall >= 1) ->
  rainy_days

Using the forward assignment operator tends to hide the final variable into which the assignment is made. This important side effect of the series of commands, the assignment to rainy_days, could easily be missed unlike our use of the backward assignment earlier.

When using the forward assignment be sure to un-indent the final variable name so that the assignment is clearer and the un-indented variable name serves as the final bracket for the command pipeline.

ds %>% 
  select(min_temp, max_temp, rainfall, sunshine) %>%
  filter(rainfall >= 1) ->
rainy_days

An intermediate value can also be assigned in the midst of a pipeline using base::assign():

ds %>% 
  select(min_temp, max_temp, rainfall, sunshine) %T>%
  assign("intermediate", ., globalenv()) %>%
  filter(rainfall >= 1) ->
rainy_days

A side track processing of the data can also be assigned as an intermediate:

ds %>% 
  select(min_temp, max_temp, rainfall, sunshine) %T>%
  {assign("all_days_rain", . %>% select(rainfall), globalenv()) %>%
  filter(rainfall >= 1) ->
rainy_days

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