glue

Overview

Glue offers interpreted string literals that are small, fast, and dependency-free. Glue does this by embedding R expressions in curly braces which are then evaluated and inserted into the argument string.

Installation

# Install the released version from CRAN:
install.packages("glue")

Install the development version from GitHub:
install.packages("devtools")
devtools::install_github("tidyverse/glue")

Usage

Variables can be passed directly into strings.

library(glue)
name  My name is Fred.

Long strings are broken by line and concatenated together.

library(glue)

name  My name is Fred, my age next year is 51, my anniversary is Saturday, October 12, 1991.

Named arguments are used to assign temporary variables.

glue('My name is {name},',
  ' my age next year is {age + 1},',
  ' my anniversary is {format(anniversary, "%A, %B %d, %Y")}.',
  name = "Joe",
  age = 40,
  anniversary = as.Date("2001-10-12"))
#> My name is Joe, my age next year is 41, my anniversary is Friday, October 12, 2001.

glue_data()

is useful with magrittr pipes.

`%>%` %`
head(mtcars) %>% glue_data("{rownames(.)} has {hp} hp")
#> Mazda RX4 has 110 hp
#> Mazda RX4 Wag has 110 hp
#> Datsun 710 has 93 hp
#> Hornet 4 Drive has 110 hp
#> Hornet Sportabout has 175 hp
#> Valiant has 105 hp

Or within dplyr pipelines

library(dplyr)
head(iris) %>%
  mutate(description = glue("This {Species} has a petal length of {Petal.Length}"))
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> 1          5.1         3.5          1.4         0.2  setosa
#> 2          4.9         3.0          1.4         0.2  setosa
#> 3          4.7         3.2          1.3         0.2  setosa
#> 4          4.6         3.1          1.5         0.2  setosa
#> 5          5.0         3.6          1.4         0.2  setosa
#> 6          5.4         3.9          1.7         0.4  setosa
#>                             description
#> 1 This setosa has a petal length of 1.4
#> 2 This setosa has a petal length of 1.4
#> 3 This setosa has a petal length of 1.3
#> 4 This setosa has a petal length of 1.5
#> 5 This setosa has a petal length of 1.4
#> 6 This setosa has a petal length of 1.7

Leading whitespace and blank lines from the first and last lines are automatically trimmed.

This lets you indent the strings naturally in code.

glue("
    A formatted string
    Can have multiple lines
      with additional indention preserved
    ")
#> A formatted string
#> Can have multiple lines
#>   with additional indention preserved

An additional newline can be used if you want a leading or trailing newline.

glue("

  leading or trailing newlines can be added explicitly
  ")
#> 
#> leading or trailing newlines can be added explicitly

\\

at the end of a line continues it without a new line.

glue("
    A formatted string \\
    can also be on a \\
    single line
    ")
#> A formatted string can also be on a single line

A literal brace is inserted by using doubled braces.

name  My name is Fred, not {name}.

Alternative delimiters can be specified with

.open

and

.close

.

one >$.", .open = "<>")
#> The value of $e^{2\pi i}$ is $1$.

All valid R code works in expressions, including braces and escaping.

Backslashes do need to be doubled just like in all R strings.

  `foo}\``  foo

glue_sql()

makes constructing SQL statements safe and easy

Use backticks to quote identifiers, normal strings and numbers are quoted appropriately for your backend.

library(glue)

con  {num}
    AND {tbl}.species = {val}
  ", .con = con)
#>  SELECT sepal_width
#> FROM iris
#> WHERE iris.sepal_length > 2
#>   AND iris.species = 'setosa'
glue_sql() can be used in conjunction with parameterized queries using
DBI::dbBind() to provide protection for SQL Injection attacks
 sql  ?
  ", .con = con)
query    sepal_width
#> 1         3.5
#> 2         3.0
#> 3         3.2
#> 4         3.1
DBI::dbClearResult(query)
glue_sql() can be used to build up more complex queries with
interchangeable sub queries. It returns DBI::SQL() objects which are
properly protected from quoting.
sub_query   SELECT s.sepal_width
#> FROM (SELECT *
#> FROM iris) AS s
If you want to input multiple values for use in SQL IN statements put *
at the end of the value and the values will be collapsed and quoted appropriately.
glue_sql("SELECT * FROM {tbl} WHERE sepal_length IN ({vals*})",
  vals = 1, .con = con)
#>  SELECT * FROM iris WHERE sepal_length IN (1)
glue_sql("SELECT * FROM {tbl} WHERE sepal_length IN ({vals*})",
  vals = 1:5, .con = con)
#>  SELECT * FROM iris WHERE sepal_length IN (1, 2, 3, 4, 5)
glue_sql("SELECT * FROM {tbl} WHERE species IN ({vals*})",
  vals = "setosa", .con = con)
#>  SELECT * FROM iris WHERE species IN ('setosa')
glue_sql("SELECT * FROM {tbl} WHERE species IN ({vals*})",
  vals = c("setosa", "versicolor"), .con = con)
#>  SELECT * FROM iris WHERE species IN ('setosa', 'versicolor')

Optionally combine strings with

+

x  x + y = 4

Other implementations

Some other implementations of string interpolation in R (although not using identical syntax).

• stringr::str_interp
• pystr::pystr_format
• R.utils::gstring
• rprintf

String templating is closely related to string interpolation, although not exactly the same concept. Some packages implementing string templating in R include.

• whisker
• brew

Code of Conduct

Please note that the glue project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.