I have equations defined likef<-"x^2"and g<-"y^2". I want to obtain equation z like z<-(x^2)*(y^2).
'Class(f)', 'class(g)' and 'class(z)' values doesn`t matter for me.
I tried this:
> f<-"x^2"
> g<-"y^2"
> z<-f*g
I got:
Error in f * g : non-numeric argument to binary operator<br/>
I tried multiplying f<-expression(f) and g<-expression(g) with no result.
I tried also:
> f<-function(x) x^2
> g<-function(y) y^2
> z<-function(x,y) f*g
> z<-parse(text=z)
I got:
Error in as.character(x) :
cannot coerce type 'closure' to vector of type 'character'
With paste(z) instead of parse(z):
> paste(z)
Error in paste(z) :
cannot coerce type 'closure' to vector of type 'character'
Is there a way to do symbolic arithmetics with equations in R without using heavy software like yacas?
You could try the following:
f <- expression(x^2)
g <- expression(y^2)
z <- expression(eval(f) * eval(g))
#> eval(z,list(x = 1, y = 2))
#[1] 4
#...and here's another test, just to be sure:
#> identical(eval(z, list(x = 17, y = 21)), 17^2 * 21^2)
#[1] TRUE
Or you could use the rSymPy package:
library(rSymPy)
x <- Var("x")
y <- Var("y")
sympy("f = x**2")
sympy("g = y**2")
sympy("z = f * g")
#> sympy("z")
#[1] "x**2*y**2"
#> sympy("z.subs([(x,3),(y,2)])")
#[1] "36"
This second suggestion might not be very attractive since it may be easier to use Python directly.
Your use of symbols and functions is very confusing. If you want to use "pieces" of language objects, you would use something more like
f <- quote(x^2)
g <- quote(y^2)
z <- quote(f*g)
do.call("substitute", list(z, list(f=f, g=g)))
# x^2 * y^2
If you just want some form of functional composition, just make sure you are treating your variables like functions
f <- function(x) x^2
g <- function(y) y^2
z <- function(x,y) f(x)*g(y)
But these are just methods of building R language elements. It's not wise to think of these as algebraic manipulations. R will make no attempt to simplify or anything like that.
