I am using gsub in R to add text into the middle of a string. It works perfectly but for some reason, when the location gets too long it throws an error. The code is below:
gsub(paste0('^(.{', as.integer(loc[1])-1, '})(.+)$'), new_cols, sql)
Error in gsub(paste0("^(.{273})(.+)$"), new_cols, sql) : invalid regular expression '^(.{273})(.+)$', reason 'Invalid contents of {}'
This code works fine when the number in the brackets(273 in this case) is less but not when it is this large.
This produces the error:
sql <- "The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats.The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats."
new_cols <- "happy"
gsub('^(.{125})(.+)$', new_cols, sql) #**Works
gsub('^(.{273})(.+)$', new_cols, sql)
Error in gsub("^(.{273})(.+)$", new_cols, sql) : invalid regular expression '^(.{273})(.+)$', reason 'Invalid contents of {}'
R gsub
uses TRE regex library by default. The boundaries in the limiting quantifier are valid from 0 till RE_DUP_MAX
that is defined in the TRE code. See this TRE reference :
A bound is one of the following, where
n
andm
are unsigned decimal integers between0
andRE_DUP_MAX
It seems that the RE_DUP_MAX
is set to 255 (see this TRE source file showing #define RE_DUP_MAX 255
), and thus, you cannot use more in {n,m}
limiting quantifier.
Use PCRE regex flavor, add perl = TRUE
and it will work.
R demo :
> sql <- "The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats.The cat with the bat went to town. He ate the fat mat and wouldn't stop til the sun came up. He was a fat cat that lived with a rat who owned many hats."
> new_cols <- "happy"
> gsub('^(.{273})(.+)$', new_cols, sql, perl=TRUE)
[1] "happy"
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