# 9Using pipes, i.e. %>% and |>

## 9.1 Intro to the “pipe”, i.e. %>% from the magrittr package

# The pipe symbol, i.e. %>% that we will be discussing below
# is part of the magrittr package. You can install/load magrittr directly.
# Alternatively, magrittr is automatically installed/loaded with most of the
# tidyverse packages.
if(!require(magrittr)) {install.packages("magrittr");require(magrittr);}
#
# help(package="magrittr")`

## 9.2 Using the %>% operator.

The %>% operator is used to send the output of one command into the into a 2nd commmand. Specifically, the info on the left side of the %>% is sent into the first argument of the function on the right hand side of the %>% See the example below.

# The following is code that does NOT use a "pipe".
x = seq(4,6)
rep(x, 3)
[1] 4 5 6 4 5 6 4 5 6
# The following code uses a "pipe", i.e. %>%, to send
# the info from the left of the %>% into the first argument
# of the function that appears on the right hand side
# of the %>%
seq(4, 6) %>% rep(3)
[1] 4 5 6 4 5 6 4 5 6
# We can extend this further
seq(4, 6)  %>%  rep(3)  %>%  sum()
[1] 45
# To make it easier to read, we can put each function
# call on a separate line.
seq(4, 6) %>%
rep(3) %>%
sum()
[1] 45
# Notice in the code above that the %>% appears at the end of
# each line. This is necessary to indicate to R that the command
# isn't finished yet.

# Without pipes, we could have coded the same thing using the
# following R code. This still works but the pipes make it easier
# to read and understand the code.

x = seq(4,6)
y = rep(x, 3)
sum(y)
[1] 45

## 9.3 Passing a value to an argument that is not the 1st argument

If you want to send a value to an argument that is not the first, you can use the period as shown in the code below.

# define a vector of numbers
nums = c(1,3)

# This is without the pipe:
rep("hello", sum(nums))
[1] "hello" "hello" "hello" "hello"
# This is with the pipe. We use the . in the rep function to show
# where the output of the pipe should go.

sum(nums) %>%
rep("hello", .)
[1] "hello" "hello" "hello" "hello"

## 9.4 You can also use the |> operator

The %>% was and is still part of the magrittr package. The pipe was seen as such a useful tool that as of R version 4.1 “base-R” started to include its own version of the pipe. The base-R version of the pipe is |> while the magrittr version of the pipe is %>%

The pipe symbol that is now built into R (without needing to load the magrittr package) provides basic pipe functionality. However, if you want extra features (e.g. using the . to show where the data should be placed) then you still need to use the magrittr version of the pipe.

# The following is the new base-R version of the pipe
seq(4, 6) |>
rep(3) |>
sum()
[1] 45
# Unfortunately you cannot use |> to send the output to any location
# other than the 1st argument. For example:
nums = c(1,3)

# this doesn't work:
sum(nums) |>        # using the new base-R pipe symbol |>
rep("hello", .)