Package 'glue'

Description

A glue object is a character vector with S3 class "glue". The "glue" class implements a print method that shows the literal contents (rather than the string implementation) and a + method, so that you can concatenate with the addition operator.

Usage

as_glue(x, ...)

Arguments

Value

A character vector with S3 class "glue".

Examples

x <- as_glue(c("abc", "\"\\\\", "\n"))
x

x <- 1
y <- 3
glue("x + y") + " = {x + y}"

Description

Expressions enclosed by braces will be evaluated as R code. Long strings are broken by line and concatenated together. Leading whitespace and blank lines from the first and last lines are automatically trimmed.

Usage

glue_data(
  .x,
  ...,
  .sep = "",
  .envir = parent.frame(),
  .open = "{",
  .close = "}",
  .na = "NA",
  .null = character(),
  .comment = "#",
  .literal = FALSE,
  .transformer = identity_transformer,
  .trim = TRUE
)

glue(
  ...,
  .sep = "",
  .envir = parent.frame(),
  .open = "{",
  .close = "}",
  .na = "NA",
  .null = character(),
  .comment = "#",
  .literal = FALSE,
  .transformer = identity_transformer,
  .trim = TRUE
)

Arguments

Value

A glue object, as created by as_glue().

See Also

https://www.python.org/dev/peps/pep-0498/ and https://www.python.org/dev/peps/pep-0257/ upon which this is based.

Examples

name <- "Fred"
age <- 50
anniversary <- as.Date("1991-10-12")
glue('My name is {name},',
  'my age next year is {age + 1},',
  'my anniversary is {format(anniversary, "%A, %B %d, %Y")}.')

# single braces can be inserted by doubling them
glue("My name is {name}, not {{name}}.")

# Named arguments can be 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"))

# `glue()` can also be used in user defined functions
intro <- function(name, profession, country){
  glue("My name is {name}, a {profession}, from {country}")
}
intro("Shelmith", "Senior Data Analyst", "Kenya")
intro("Cate", "Data Scientist", "Kenya")

# `glue_data()` is useful in magrittr pipes
if (require(magrittr)) {

mtcars %>% glue_data("{rownames(.)} has {hp} hp")

# Or within dplyr pipelines
if (require(dplyr)) {

head(iris) %>%
  mutate(description = glue("This {Species} has a petal length of {Petal.Length}"))

}}

# Alternative delimiters can also be used if needed
one <- "1"
glue("The value of $e^{2\\pi i}$ is $<<one>>$.", .open = "<<", .close = ">>")

Description

The crayon package defines a number of functions used to color terminal output. glue_col() and glue_data_col() functions provide additional syntax to make using these functions in glue strings easier.

Using the following syntax will apply the function crayon::blue() to the text 'foo bar'.

{blue foo bar}

If you want an expression to be evaluated, simply place that in a normal brace expression (these can be nested).

{blue 1 + 1 = {1 + 1}}

If the text you want to color contains, e.g., an unpaired quote or a comment character, specify .literal = TRUE.

Usage

glue_col(..., .envir = parent.frame(), .na = "NA", .literal = FALSE)

glue_data_col(.x, ..., .envir = parent.frame(), .na = "NA", .literal = FALSE)

Arguments

Value

A glue object, as created by as_glue().

Examples

library(crayon)

glue_col("{blue foo bar}")

glue_col("{blue 1 + 1 = {1 + 1}}")

glue_col("{blue 2 + 2 = {green {2 + 2}}}")

white_on_black <- bgBlack $ white
glue_col("{white_on_black
  Roses are {red {colors()[[552]]}},
  Violets are {blue {colors()[[26]]}},
  `glue_col()` can show \\
  {red c}{yellow o}{green l}{cyan o}{blue r}{magenta s}
  and {bold bold} and {underline underline} too!
}")

# this would error due to an unterminated quote, if we did not specify
# `.literal = TRUE`
glue_col("{yellow It's} happening!", .literal = TRUE)

# `.literal = TRUE` also prevents an error here due to the `#` comment
glue_col(
  "A URL: {magenta https://github.com/tidyverse/glue#readme}",
  .literal = TRUE
)

# `.literal = TRUE` does NOT prevent evaluation
x <- "world"
y <- "day"
glue_col("hello {x}! {green it's a new {y}!}", .literal = TRUE)

Description

glue_collapse() collapses a character vector of any length into a length 1 vector. glue_sql_collapse() does the same but returns a ⁠[DBI::SQL()]⁠ object rather than a glue object.

Usage

glue_collapse(x, sep = "", width = Inf, last = "")

glue_sql_collapse(x, sep = "", width = Inf, last = "")

Arguments

Value

Always returns a length-1 glue object, as created by as_glue().

Examples

glue_collapse(glue("{1:10}"))

# Wide values can be truncated
glue_collapse(glue("{1:10}"), width = 5)

glue_collapse(1:4, ", ", last = " and ")

Description

glue_safe() and glue_data_safe() differ from glue() and glue_data() in that the safe versions only look up symbols from an environment using get(). They do not execute any R code. This makes them suitable for use with untrusted input, such as inputs in a Shiny application, where using the normal functions would allow an attacker to execute arbitrary code.

Usage

glue_safe(..., .envir = parent.frame())

glue_data_safe(.x, ..., .envir = parent.frame())

Arguments

Value

A glue object, as created by as_glue().

Examples

"1 + 1" <- 5
# glue actually executes the code
glue("{1 + 1}")

# glue_safe just looks up the value
glue_safe("{1 + 1}")

rm("1 + 1")

Description

SQL databases often have custom quotation syntax for identifiers and strings which make writing SQL queries error prone and cumbersome to do. glue_sql() and glue_data_sql() are analogs to glue() and glue_data() which handle the SQL quoting. glue_sql_collapse() can be used to collapse DBI::SQL() objects.

They automatically quote character results, quote identifiers if the glue expression is surrounded by backticks '⁠`⁠' and do not quote non-characters such as numbers. If numeric data is stored in a character column (which should be quoted) pass the data to glue_sql() as a character.

Returning the result with DBI::SQL() will suppress quoting if desired for a given value.

Note parameterized queries are generally the safest and most efficient way to pass user defined values in a query, however not every database driver supports them.

If you place a * at the end of a glue expression the values will be collapsed with commas, or if there are no values, produce NULL. This is useful for (e.g.) the SQL IN Operator.

Usage

glue_sql(
  ...,
  .con,
  .sep = "",
  .envir = parent.frame(),
  .open = "{",
  .close = "}",
  .na = DBI::SQL("NULL"),
  .null = character(),
  .comment = "#",
  .literal = FALSE,
  .trim = TRUE
)

glue_data_sql(
  .x,
  ...,
  .con,
  .sep = "",
  .envir = parent.frame(),
  .open = "{",
  .close = "}",
  .na = DBI::SQL("NULL"),
  .null = character(),
  .comment = "#",
  .literal = FALSE,
  .trim = TRUE
)

Arguments

Value

A DBI::SQL() object with the given query.

See Also

glue_sql_collapse() to collapse DBI::SQL() objects.

Examples

con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
iris2 <- iris
colnames(iris2) <- gsub("[.]", "_", tolower(colnames(iris)))
DBI::dbWriteTable(con, "iris", iris2)
var <- "sepal_width"
tbl <- "iris"
num <- 2
val <- "setosa"
glue_sql("
  SELECT {`var`}
  FROM {`tbl`}
  WHERE {`tbl`}.sepal_length > {num}
    AND {`tbl`}.species = {val}
  ", .con = con)

# If sepal_length is store on the database as a character explicitly convert
# the data to character to quote appropriately.
glue_sql("
  SELECT {`var`}
  FROM {`tbl`}
  WHERE {`tbl`}.sepal_length > {as.character(num)}
    AND {`tbl`}.species = {val}
  ", .con = con)


# `glue_sql()` can be used in conjuction with parameterized queries using
# `DBI::dbBind()` to provide protection for SQL Injection attacks
 sql <- glue_sql("
    SELECT {`var`}
    FROM {`tbl`}
    WHERE {`tbl`}.sepal_length > ?
  ", .con = con)
query <- DBI::dbSendQuery(con, sql)
DBI::dbBind(query, list(num))
DBI::dbFetch(query, n = 4)
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 <- glue_sql("
  SELECT *
  FROM {`tbl`}
  ", .con = con)

glue_sql("
  SELECT s.{`var`}
  FROM ({sub_query}) AS s
  ", .con = con)

# 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)

glue_sql("SELECT * FROM {`tbl`} WHERE sepal_length IN ({vals*})",
  vals = 1:5, .con = con)

glue_sql("SELECT * FROM {`tbl`} WHERE species IN ({vals*})",
  vals = "setosa", .con = con)

glue_sql("SELECT * FROM {`tbl`} WHERE species IN ({vals*})",
  vals = c("setosa", "versicolor"), .con = con)

# If you need to reference variables from multiple tables use `DBI::Id()`.
# Here we create a new table of nicknames, join the two tables together and
# select columns from both tables. Using `DBI::Id()` and the special
# `glue_sql()` syntax ensures all the table and column identifiers are quoted
# appropriately.

iris_db <- "iris"
nicknames_db <- "nicknames"

nicknames <- data.frame(
  species = c("setosa", "versicolor", "virginica"),
  nickname = c("Beachhead Iris", "Harlequin Blueflag", "Virginia Iris"),
  stringsAsFactors = FALSE
)

DBI::dbWriteTable(con, nicknames_db, nicknames)

cols <- list(
  DBI::Id(iris_db, "sepal_length"),
  DBI::Id(iris_db, "sepal_width"),
  DBI::Id(nicknames_db, "nickname")
)

iris_species <- DBI::Id(iris_db, "species")
nicknames_species <- DBI::Id(nicknames_db, "species")

query <- glue_sql("
  SELECT {`cols`*}
  FROM {`iris_db`}
  JOIN {`nicknames_db`}
  ON {`iris_species`}={`nicknames_species`}",
  .con = con
)
query

DBI::dbGetQuery(con, query, n = 5)

DBI::dbDisconnect(con)

Description

This is a simple wrapper around eval(parse()), used as the default transformer.

Usage

identity_transformer(text, envir = parent.frame())

Arguments

See Also

vignette("transformers", "glue") for documentation on creating custom glue transformers and some common use cases.

Description

These functions make it easy to quote each individual element and are useful in conjunction with glue_collapse(). These are thin wrappers around base::encodeString().

Usage

single_quote(x)

double_quote(x)

backtick(x)

Arguments

Value

A character vector of the same length as x, with the same attributes (including names and dimensions) but with no class set.

Marked UTF-8 encodings are preserved.

Examples

x <- 1:5
glue('Values of x: {glue_collapse(backtick(x), sep = ", ", last = " and ")}')

Description

This trims a character vector according to the trimming rules used by glue. These follow similar rules to Python Docstrings, with the following features.

• Leading and trailing whitespace from the first and last lines is removed.

• A uniform amount of indentation is stripped from the second line on, equal to the minimum indentation of all non-blank lines after the first.

• Lines can be continued across newlines by using ⁠\\⁠.

Usage

trim(x)

Arguments

Value

A character vector.

Examples

glue("
    A formatted string
    Can have multiple lines
      with additional indentation preserved
    ")

glue("
  \ntrailing or leading newlines can be added explicitly\n
  ")

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