Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Convert string to a variable name

Tags:

string

r

People also ask

How do you convert a string to a variable name in Matlab?

varname = genvarname(str) constructs a string or character vector varname that is similar to or the same as the str input, and can be used as a valid variable name. str can be a string, a string array, a character array, a cell array of character vectors.

Can we use string as a variable name in Java?

SYNTAX: String varaiable name=new String(“ “); Since Strings are classes . so,we use new keyword to create objects & to access it.

How do you assign a string to a variable in Python?

To assign it to a variable, we can use the variable name and “=” operator. Normally single and double quotes are used to assign a string with a single line of character but triple quotes are used to assign a string with multi-lines of character.


assign is what you are looking for.

assign("x", 5)

x
[1] 5

but buyer beware.

See R FAQ 7.21 http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-can-I-turn-a-string-into-a-variable_003f


You can use do.call:

 do.call("<-",list(parameter_name, parameter_value))

There is another simple solution found there: http://www.r-bloggers.com/converting-a-string-to-a-variable-name-on-the-fly-and-vice-versa-in-r/

To convert a string to a variable:

x <- 42
eval(parse(text = "x"))
[1] 42

And the opposite:

x <- 42
deparse(substitute(x))
[1] "x"

The function you are looking for is get():

assign ("abc",5)
get("abc")

Confirming that the memory address is identical:

getabc <- get("abc")
pryr::address(abc) == pryr::address(getabc)
# [1] TRUE

Reference: R FAQ 7.21 How can I turn a string into a variable?


Use x=as.name("string"). You can use then use x to refer to the variable with name string.

I don't know, if it answers your question correctly.


strsplit to parse your input and, as Greg mentioned, assign to assign the variables.

original_string <- c("x=123", "y=456")
pairs <- strsplit(original_string, "=")
lapply(pairs, function(x) assign(x[1], as.numeric(x[2]), envir = globalenv()))
ls()

assign is good, but I have not found a function for referring back to the variable you've created in an automated script. (as.name seems to work the opposite way). More experienced coders will doubtless have a better solution, but this solution works and is slightly humorous perhaps, in that it gets R to write code for itself to execute.

Say I have just assigned value 5 to x (var.name <- "x"; assign(var.name, 5)) and I want to change the value to 6. If I am writing a script and don't know in advance what the variable name (var.name) will be (which seems to be the point of the assign function), I can't simply put x <- 6 because var.name might have been "y". So I do:

var.name <- "x"
#some other code...
assign(var.name, 5)
#some more code...

#write a script file (1 line in this case) that works with whatever variable name
write(paste0(var.name, " <- 6"), "tmp.R")
#source that script file
source("tmp.R")
#remove the script file for tidiness
file.remove("tmp.R")

x will be changed to 6, and if the variable name was anything other than "x", that variable will similarly have been changed to 6.


Donate For Us

If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!