Note: this is a copy of the README file.
infuser is a simple and very basic templating engine for R. It replaces parameters within templates with specified values. Templates can be either contained in a string or in a file.
install.packages("infuser")If you want to use the most up-to-date version, install using devtools::install_github.
devtools::install_github("Bart6114/infuser")A simple Hello World example that makes use of the magrittr piping workflow.
library(infuser)
library(magrittr)
"Hello {{var1}}!" %>%
infuse(var1="world")## Hello world!Let’s have a look at an example string.
my_sql<-"SELECT * FROM Customers
WHERE Year = {{year}}
AND Month = {{month|3}};"Here the variable parameters are enclosed by {{ and }} characters. See ?infuse to use your own specification.
From now on, we suppose the character string my_sql is our template. To show the parameters requested by the template you can run the following.
library(infuser)
variables_requested(my_sql, verbose = TRUE)## Variables requested by template:## >> year## >> month (default = 3)To fill in the template simply provide the requested parameters.
infuse(my_sql, year=2016, month=8)## SELECT * FROM Customers
## WHERE Year = 2016
## AND Month = 8;You can also provide a named list with the requested parameters.
my_list<-
list(year=2016,
month=8)
infuse(my_sql, my_list)## SELECT * FROM Customers
## WHERE Year = 2016
## AND Month = 8;If a default value is available in the template, it will be used if the parameter is not specified.
infuse(my_sql, year=2016)## SELECT * FROM Customers
## WHERE Year = 2016
## AND Month = 3;Just like we’re using a string here, a text file can be used. An example text file can be found in the package as follows:
example_file<-
system.file("extdata", "sql1.sql", package="infuser")
example_file## [1] "/private/var/folders/th/n7_sp4sx5073fjg9qzcx0gvr0000gn/T/Rtmp8mrLJw/Rinstd20ca7c24ff/infuser/extdata/sql1.sql"Again, we can check which parameters are requested by the template.
variables_requested(example_file, verbose = TRUE)## Variables requested by template:## >> month (default = 3)## >> yearAnd provide their values.
infuse(example_file, year = 2016, month = 12)## SELECT LAT_N, CITY, TEMP_F
## FROM STATS, STATION
## WHERE MONTH = 12
## AND YEAR = 2016
## AND STATS.ID = STATION.ID
## ORDER BY TEMP_F;It is quite easy to infuse a vector.
years <- c(2013,2014,2015)
sql_string <- "SELECT * FROM T1 WHERE Year IN ({{years}})"
infuse(sql_string, years=years)## SELECT * FROM T1 WHERE Year IN (2013,2014,2015)You can also specify the collapse character.
infuse(sql_string, years=years, collapse_char = ";")## SELECT * FROM T1 WHERE Year IN (2013;2014;2015)A transform_function can be specified in the infuse command. This allows for pre-processing of the parameter values before inserting them in the template.
What we don’t want to happen is the following:
sql<-"INSERT INTO Students (Name) VALUES ({{name}})"
name <- "Robert'); DROP TABLE Students;--"
infuse(sql, name = name)## INSERT INTO Students (Name) VALUES (Robert'); DROP TABLE Students;--)Yikes! A way to solve this is to specify your own custom transform function.
my_transform_function<-function(v){
# replace single quotes with double quotes
v<-gsub("'", "''", v)
# encloses the string in single quotes
v<-paste0("'",v,"'")
return(v)
}
infuse(sql, name = name, transform_function = my_transform_function)## INSERT INTO Students (Name) VALUES ('Robert''); DROP TABLE Students;--')Of course you can also use functions from other packages. Specifically for SQL I advise you to take a look at the dbplyr::build_sql function.
infuse(sql, name = name, transform_function = dbplyr::build_sql)## Warning: Installed Rcpp (0.12.12) different from Rcpp used to build dplyr (0.12.11).
## Please reinstall dplyr to avoid random crashes or undefined behavior.## INSERT INTO Students (Name) VALUES ('Robert''); DROP TABLE Students;--')