Excel RegEx Functions in R - regex

Question

I regularly work with Excel Sheets where some fields (observations) contain large amounts of text content in a part structured form (at least visually)
So the content of a single Cell/Obs might be somewhat like this:
My name is John Doe
I live at my address
My Post code is ABC123
My Favorite Pet is: A dog
In Excel I've created a few functions which I can use to look for a string within the cell so lets say that the data is in "A1"
in "A2" I can use "=GETPOSTCODE(A1) where the function is:
Function GetPostCode(PostCode As Range) As String
regex.Pattern = "[A-Z]{3}\d{3,}\b\w*"
regex.IgnoreCase = True
regex.MultiLine = True
Set X = regex.Execute(PostCode.Value)
For Each x1 In X
GetPostCode = UCase(x1)
Exit For
Next
End Function
What kind of structures/functions could I use in r to accomplish this?
the Cells really contain Much more data than that, its purely for example, and I have a number of different "get" functions with different regexs.
I've had a good look at all the Grep type commands but am struggling with limited/developing R skills.
I've been working around this kind of Principle, but pretty much stalled (where textfield is the column with my text in obviously!) I can get a list of all the rows where it contains a post code but not JUST the Post Code:
df$postcode <- df[(df$textfield = grep("[A-Z]{3}\\d{3,}\\b\\w*", df$textfield), ]
Any Help appreciated!

Answer 1

I think you need a combination of regexpr or grepexpr (to find the matches in the string) and regmatches to extract the matching parts of the strings:
x <- "My name is John Doe
I live at my address
My Post code is ABC123
My Favorite Pet is: A dog"
> regmatches(x, regexpr("[A-Z]{3}\\d{3,}\\b\\w*", x, ignore.case = TRUE))
[1] "ABC123"
Other options probably include str_extract from stringr or stri_extract from stringi packages.