String interpolation is a useful way of specifying a character string which
depends on values in a certain environment. It allows for string creation
which is easier to read and write when compared to using e.g.
paste() or sprintf(). The (template) string can
include expression placeholders of the form ${expression} or
$[format]{expression}, where expressions are valid R expressions that
can be evaluated in the given environment, and format is a format
specification valid for use with sprintf().
str_interp(string, env = parent.frame())A template character string. This function is not vectorised: a character vector will be collapsed into a single string.
The environment in which to evaluate the expressions.
An interpolated character string.
str_glue() and str_glue_data() for alternative approaches to
the same problem.
# NOT RUN {
# Using values from the environment, and some formats
user_name <- "smbache"
amount <- 6.656
account <- 1337
str_interp("User ${user_name} (account $[08d]{account}) has $$[.2f]{amount}.")
# Nested brace pairs work inside expressions too, and any braces can be
# placed outside the expressions.
str_interp("Works with } nested { braces too: $[.2f]{{{2 + 2}*{amount}}}")
# Values can also come from a list
str_interp(
"One value, ${value1}, and then another, ${value2*2}.",
list(value1 = 10, value2 = 20)
)
# Or a data frame
str_interp(
"Values are $[.2f]{max(Sepal.Width)} and $[.2f]{min(Sepal.Width)}.",
iris
)
# Use a vector when the string is long:
max_char <- 80
str_interp(c(
"This particular line is so long that it is hard to write ",
"without breaking the ${max_char}-char barrier!"
))
# }