CODEWITHSUNDEEP
r
wxyz
wxyz

Reputation: 35

extract coefficients of polynomial expression

a="1-B*(0.5+c1)+B**2*(-c2+0.5*c1)+0.5*c3*B**3"

I want to breakdown the above character string as

B, -(0.5+c1), B**2, (-c2+0.5c1), B**3, 0.5*c3

using R. Any suggestions?

Upvotes: 0

Views: 280

Answers (1)

Anders Ellern Bilgrau
Anders Ellern Bilgrau

Reputation: 10233

While not exactly what you want as output, the following is sufficiently close and might help you solve the problem:

a <- "1-B*(0.5+c1)+B**2*(-c2+0.5*c1)+0.5*c3*B**3"
b <- gsub("**", "^", a, fixed = TRUE)  # Replace "**" with "^" to simply the regex

ans <- unlist(strsplit(b, '\\([^)]*\\)(*SKIP)(*F)|\\*|\\+', perl = TRUE))
print(ans)
#[1] "1-B"       "(0.5+c1)"     "B^2"     "(-c2+0.5*c1)" "0.5"          "c3"          
#[7] "B^3"

More on the regular expression used can be found here. You can easily change the "^" back to "**" using gsub.

I see no easy way to attach the negative sign of B to the coefficient.

Upvotes: 1

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