How do I convert a subsetted object character string name to a usable object in R? [duplicate]

Question

Suppose I have a character string of a subsetted object name. For example:

foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]  #is currently represented as...
"foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]"

I want to call the subsetted object using the character string of the object's name.

I tried using get():

get("foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]")

but I get the error:

Error in "foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]":
object  "foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]" not found

I'm assuming there is a way to do this using subsetted objects (vs. just an object name, which I know works).

Thanks in advance!

How did you get yourself in this situation? Putting R code into strings isn't something one might consider a good strategy in R. The get() functions returns variables of a given name, it does not evaluate code (and operations like [ and & and < are functions in R). You might be able to parse and eval, eval(parse(text=x)), but that's not something I would recommend necessarily. — MrFlick
– MrFlick, Commented Jul 27, 2015 at 19:22

Community · Accepted Answer · 2017-05-23 12:24:21Z

5

As mentioned in comments by @MrFlick, you can do this:

eval(parse(text="foo$var1[foo$var2 < 10 & foo$var3 %in% c(0:100)]"))

parse turns the string into an expression and eval evaluates that expression.

Though, this is commonly considered a bad practice in R see here

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answered Jul 27, 2015 at 19:56

Boxuan

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2 Comments

fortunes::fortune(106)

@DavidArenburg Thanks for editing! I should have read the comments more carefully.