Putting strings together with stringr

For your first stringr function, we'll look at str_c(), the c is short for concatenate, a function that works like paste(). It takes vectors of strings as input along with sep and collapse arguments.

There are two key ways str_c() differs from paste(). First, the default separator is an empty string, sep = "", as opposed to a space, so it's more like paste0(). This is an example of a stringr function, performing a similar operation to a base function, but using a default that is more likely to be what you want. Remember in your pizza order, you had to set sep = "" multiple times.

The second way str_c() differs to paste() is in its handling of missing values. paste() turns missing values into the string "NA", whereas str_c() propagates missing values. That means combining any strings with a missing value will result in another missing value.

Let's explore this difference using your pizza order from the previous chapter.

This is a part of the course

“String Manipulation with stringr in R”

View Course

Exercise instructions

We've set up a new my_toppings vector that has a few missing values and taken the first step of creating our order.

Print my_toppings_and to see what paste() did with the missing values.
Repeat the paste() statement but instead use str_c(). You can save some typing by leaving off sep = "" since that is the default. Call this string my_toppings_str.
Print my_toppings_str to see what str_c() does with the missing values.
Take the next step in our order, by using paste() on my_toppings_and with collapse = ", ".
Take the next step in our order, by using str_c() on my_toppings_str with collapse = ", ". See the difference: just one NA will make our entire result NA.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

library(stringr)

my_toppings <- c("cheese", NA, NA)
my_toppings_and <- paste(c("", "", "and "), my_toppings, sep = "")

# Print my_toppings_and
___

# Use str_c() instead of paste(): my_toppings_str
my_toppings_str <- ___

# Print my_toppings_str
___

# paste() my_toppings_and with collapse = ", "
___

# str_c() my_toppings_str with collapse = ", "
___

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