positive lookahead regex R

Question

I'm trying a regex lookahead in R with the following command:

 sub(x = street.addresses, pattern = "\\s((?i)Street|(?i)St\\.?)(?=\\sNE)", replacement = " St")

My goal is to replace Street with St where it's followed by a space and the directional NE (as in, "Northeast"). It seems like the lookahead couldn't be more straightforward but I keep hitting an error:

Error in sub(x = streets, pattern = "\\s((?i)Street|(?i)St\\.?)(?=\\sNE)",: 
invalid regular expression '\s((?i)Street|(?i)St\.?)(?=\sNE)', reason 
'Invalid regexp' 

Versions of this without the lookahead work fine in R, but as soon as I add a lookahead of any sort to my search/replace, I hit the error. Likewise, other regex R functions like grep seem to have the same problem.

I've copied/pasted that regex expression into engines like https://regex101.com/ and it seems to work fine there, so I'm confused. Am I missing something basic about regex in R?

EDIT:

Here's a copy direct from my console:

> street.addresses <- c("23 Charles Street NE","23 Charles St. NE")
> new.vec <- sub(x = street.addresses, pattern = "\\s((?i)Street|(?i)St\\.?)
(?=\\sNE)", replacement = " St")
Error in sub(x = street.addresses, pattern = "\\s((?i)Street|(?i)St\\.?)(?
=\\sNE)",  : 
invalid regular expression '\s((?i)Street|(?i)St\.?)(?=\sNE)', reason 
'Invalid regexp'

Answer 1

You need to use sub in Perl mode if you want to use a lookahead:

street <- "123 Hudson Street NE, New York, NY"
sub(x = street, pattern = "\\s((?i)Street|(?i)St\\.?)(?=\\sNE)",
    replacement = " St", perl=TRUE)

[1] "123 Hudson St NE, New York, NY"

Demo

By the way, if you put the parameters to sub in their default positions, then you can omit the names, leaving us with a more terse call:

sub("\\s((?i)Street|(?i)St\\.?)(?=\\sNE)", " St", street, perl=TRUE)