How to obtain all the variables in an R code expression?

Question

How can an expression in R be decoded to get all the variables involved?

For example if you have:

z<-x+y;

get_all_variables(z);

[1] \'x\' \'y\'
         


        

Answer 1

So far as I know, you would need to store the expression in a string. Then you can parse it with getParseData:

txt <- "z<-x+y"

sf <- srcfile("txt")   
df = getParseData(sf)    
df$text[df$token=="SYMBOL"][2:3]

For further edification, here is what the result of getParseData looks like in its entirety:

   line1 col1 line2 col2 id parent       token terminal text
11     1    1     1    6 11      0        expr    FALSE     
1      1    1     1    1  1      3      SYMBOL     TRUE    z
3      1    1     1    1  3     11        expr    FALSE     
2      1    2     1    3  2     11 LEFT_ASSIGN     TRUE   <-
10     1    4     1    6 10     11        expr    FALSE     
4      1    4     1    4  4      6      SYMBOL     TRUE    x
6      1    4     1    4  6     10        expr    FALSE     
5      1    5     1    5  5     10         '+'     TRUE    +
7      1    6     1    6  7      9      SYMBOL     TRUE    y
9      1    6     1    6  9     10        expr    FALSE