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!" )) # }