Inserting characters around a part of a string?-CodePudding

I'm looking to wrap parts of a string in R, following certain rules, in a vectorised way.

Put simply, if I had a vector:

c("x^2", "x^2:z", "z", "x:z", "z:x:b", "z:x^2:b")

the function would sweep through each element and wrap I() around those parts where there is an exponent, resulting in the following output:

c("I(x^2)", "I(x^2):z", "z", "x:z", "z:x:b", "z:I(x^2):b")

I've tried various approaches where I first split by : and then gsub, but this isn't particularly scalable.

CodePudding user response：

Something like below?

> gsub("(x(\\^\\d ))", "I(\\1)", c("x^2", "x^2:z", "z", "x:z", "z:x:b", "z:x^2:b"))
[1] "I(x^2)"     "I(x^2):z"   "z"          "x:z"        "z:x:b"     
[6] "z:I(x^2):b"

CodePudding user response：

These seem reasonably general. They don't assume that the variable in the complex fields must be named x but handle any names made of word characters and also don't assume that the arithmetic expression must be an exponential but handle any arithmetic expression that includes non-word characters. for example, they would surround y pi with I(...).

1) This one liner captures each field and processes it using the indicated function, expressed in formula notation. It surrounds each field that contains a non-word character with I(...) . It works with any variables whose names are made from word character.

library(gsubfn)

gsubfn("[^:] ", ~ if (grepl("\\W", x)) sprintf("I(%s)", x) else x, s)
## [1] "I(x^2)"     "I(x^2):z"   "z"          "x:z"        "z:x:b"     
## [6] "z:I(x^2):b"

2) This surrounds any field containing a character that is not :, letter or number with I(...)

gsub("([^:]*[^:[:alnum:]][^:]*)", "I(\\1)", s)
## [1] "I(x^2)"     "I(x^2):z"   "z"          "x:z"        "z:x:b"     
## [6] "z:I(x^2):b"

3) In this alternative we split the strings at colon, then surround fields containing a non-word character with I(...) and paste them back together.

surround <- function(x) ifelse(grepl("\\W", x), sprintf("I(%s)", x), x)
s |> 
  strsplit(":") |>
  sapply(function(x) paste(surround(x), collapse = ":"))
## [1] "I(x^2)"     "I(x^2):z"   "z"          "x:z"        "z:x:b"     
## [6] "z:I(x^2):b"

Note

The input used is the following:

s <- c("x^2", "x^2:z", "z", "x:z", "z:x:b", "z:x^2:b")