EDIT: For anyone interested, I completed my little project here and it can be seen at this link http://fdrennan.net/pages/myCurve.html Scroll down to "I think it's been generalized decently" to see the curve_fitter function. If you find it useful, steal it and I don't need credit. I still have ncol as an input but it isn't required anymore. I just didn't delete it.
I am writing a script that will do some least squares stuff for me. I'll be using it to fit curves but want to generalize it. I want to be able to write in "x, x^2" in a function and have it pasted into a matrix function and read. Here is what I am talking about.
expressionInput <- function(func = "A written function", x = "someData",
nCol = "ncol") {
# Should I coerce the sting to something in order to make...
func <- as.SOMETHING?(func)
# ...this line to be equivalent to ...
A <- matrix(c(rep(1, length(x)), func), ncol = nCol)
# .... this line
# A <- matrix(c(rep(1, length(x)), x, x^2), ncol = 3)
A
}
expressionInput(func = "x, x^2", x = 1:10, nCol = 3)
Returns 10 x 3 matrix with 1's in one column, x in second, and squared values in third column.
The link below will show a few different functions for curve fitting. The idea behind this post is to be able to write in "x + x^2" or "x + sin(x)" or "e^x" etc., and return the coefficients for curve. http://fdrennan.net/pages/myCurve.html
I think you are looking for something like this
f <- function(expr="", x=NULL, nCol=3) {
expr <- unlist(strsplit(expr,","))
ex <- rep("rep(1,length(x))", nCol)
ex[1:length(expr)] <- expr
sapply(1:length(ex), function(i) eval(parse(text=ex[i])))
}
f("x, x^2", 1:10, 3)
[,1] [,2] [,3]
[1,] 1 1 1
[2,] 2 4 1
[3,] 3 9 1
[4,] 4 16 1
[5,] 5 25 1
[6,] 6 36 1
[7,] 7 49 1
[8,] 8 64 1
[9,] 9 81 1
[10,] 10 100 1
Note that, in your example, you separate the expressions to evaluate using a comma (,). Accordingly, I have used a comma to split the string into expressions. If you try passing expressions, which themselves contain commas this will fail. So, either restrict to using simple expressions without commas. Or if this is not possible then use a different character to separate the expressions (and escape it, if you need that character to be evaluated).
However, I would also reiterate the warnings in the comments to your question that depending on what you are trying to achieve, there are likely better ways to do it.