How to insert a character every n characters from end of string





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I would like to insert a colon every five characters starting from the end of the string, preferably using regex and gsub in R.



text <- "My Very Enthusiastic Mother Just Served Us Noodles!"


I have been able to insert a colon every five characters from beginning of the text using:



gsub('(.{5})', "\1:", text, perl = T)


I have written an inelegant function for achieving this as follows:



library(dplyr)

str_reverse<-function(x){

  strsplit(x,split='')[[1]] %>% rev() %>% paste(collapse = "") 

}



text2<-str_reverse(text)

text3<-gsub('(.{5})', "\1:", text2, perl = T)

str_reverse(text3)


to get the desired result




[1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"




Is there a way this can be achieved directly using regular expressions?






r regex







share|improve this question

























  • Consider that the stringi package has the stri_reverse function already available and super efficient.

    – nicola
    Nov 16 '18 at 12:45


















2















I would like to insert a colon every five characters starting from the end of the string, preferably using regex and gsub in R.



text <- "My Very Enthusiastic Mother Just Served Us Noodles!"


I have been able to insert a colon every five characters from beginning of the text using:



gsub('(.{5})', "\1:", text, perl = T)


I have written an inelegant function for achieving this as follows:



library(dplyr)

str_reverse<-function(x){

  strsplit(x,split='')[[1]] %>% rev() %>% paste(collapse = "") 

}



text2<-str_reverse(text)

text3<-gsub('(.{5})', "\1:", text2, perl = T)

str_reverse(text3)


to get the desired result




[1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"




Is there a way this can be achieved directly using regular expressions?






r regex







share|improve this question

























  • Consider that the stringi package has the stri_reverse function already available and super efficient.

    – nicola
    Nov 16 '18 at 12:45














2












2








2








I would like to insert a colon every five characters starting from the end of the string, preferably using regex and gsub in R.



text <- "My Very Enthusiastic Mother Just Served Us Noodles!"


I have been able to insert a colon every five characters from beginning of the text using:



gsub('(.{5})', "\1:", text, perl = T)


I have written an inelegant function for achieving this as follows:



library(dplyr)

str_reverse<-function(x){

  strsplit(x,split='')[[1]] %>% rev() %>% paste(collapse = "") 

}



text2<-str_reverse(text)

text3<-gsub('(.{5})', "\1:", text2, perl = T)

str_reverse(text3)


to get the desired result




[1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"




Is there a way this can be achieved directly using regular expressions?






r regex







share|improve this question
















I would like to insert a colon every five characters starting from the end of the string, preferably using regex and gsub in R.



text <- "My Very Enthusiastic Mother Just Served Us Noodles!"


I have been able to insert a colon every five characters from beginning of the text using:



gsub('(.{5})', "\1:", text, perl = T)


I have written an inelegant function for achieving this as follows:



library(dplyr)

str_reverse<-function(x){

  strsplit(x,split='')[[1]] %>% rev() %>% paste(collapse = "") 

}



text2<-str_reverse(text)

text3<-gsub('(.{5})', "\1:", text2, perl = T)

str_reverse(text3)


to get the desired result




[1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"




Is there a way this can be achieved directly using regular expressions?






r regex




r regex






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 16 '18 at 12:29









Sotos

31.2k51741




31.2k51741










asked Nov 16 '18 at 12:14









Joseph KigothoJoseph Kigotho

226




226













  • Consider that the stringi package has the stri_reverse function already available and super efficient.

    – nicola
    Nov 16 '18 at 12:45



















  • Consider that the stringi package has the stri_reverse function already available and super efficient.

    – nicola
    Nov 16 '18 at 12:45

















Consider that the stringi package has the stri_reverse function already available and super efficient.

– nicola
Nov 16 '18 at 12:45





Consider that the stringi package has the stri_reverse function already available and super efficient.

– nicola
Nov 16 '18 at 12:45












1 Answer
1






active

oldest

votes


















4














You may use



gsub('(?=(?:.{5})+$)', ":", text, perl = TRUE)

## => [1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"


See the regex demo



The (?=(?:.{5})+$) pattern matches any location inside the string that is followed with any 5 chars (other than line break chars) 1 or more times up to the end of the string.



If the input string can contain line breaks you need to add (?s) at the start of the pattern (since . in PCRE regex does not match line breaks by default):



'(?s)(?=(?:.{5})+$)'





share|improve this answer



















  • 1





    @AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:46











  • thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

    – Andre Elrico
    Nov 16 '18 at 12:49











  • @AndreElrico You may want to read my quantfier explanations, too.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:53














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1 Answer
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1 Answer
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active

oldest

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active

oldest

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oldest

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4














You may use



gsub('(?=(?:.{5})+$)', ":", text, perl = TRUE)

## => [1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"


See the regex demo



The (?=(?:.{5})+$) pattern matches any location inside the string that is followed with any 5 chars (other than line break chars) 1 or more times up to the end of the string.



If the input string can contain line breaks you need to add (?s) at the start of the pattern (since . in PCRE regex does not match line breaks by default):



'(?s)(?=(?:.{5})+$)'





share|improve this answer



















  • 1





    @AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:46











  • thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

    – Andre Elrico
    Nov 16 '18 at 12:49











  • @AndreElrico You may want to read my quantfier explanations, too.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:53


















4














You may use



gsub('(?=(?:.{5})+$)', ":", text, perl = TRUE)

## => [1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"


See the regex demo



The (?=(?:.{5})+$) pattern matches any location inside the string that is followed with any 5 chars (other than line break chars) 1 or more times up to the end of the string.



If the input string can contain line breaks you need to add (?s) at the start of the pattern (since . in PCRE regex does not match line breaks by default):



'(?s)(?=(?:.{5})+$)'





share|improve this answer



















  • 1





    @AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:46











  • thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

    – Andre Elrico
    Nov 16 '18 at 12:49











  • @AndreElrico You may want to read my quantfier explanations, too.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:53
















4












4








4







You may use



gsub('(?=(?:.{5})+$)', ":", text, perl = TRUE)

## => [1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"


See the regex demo



The (?=(?:.{5})+$) pattern matches any location inside the string that is followed with any 5 chars (other than line break chars) 1 or more times up to the end of the string.



If the input string can contain line breaks you need to add (?s) at the start of the pattern (since . in PCRE regex does not match line breaks by default):



'(?s)(?=(?:.{5})+$)'





share|improve this answer













You may use



gsub('(?=(?:.{5})+$)', ":", text, perl = TRUE)

## => [1] "M:y Ver:y Ent:husia:stic :Mothe:r Jus:t Ser:ved U:s Noo:dles!"


See the regex demo



The (?=(?:.{5})+$) pattern matches any location inside the string that is followed with any 5 chars (other than line break chars) 1 or more times up to the end of the string.



If the input string can contain line breaks you need to add (?s) at the start of the pattern (since . in PCRE regex does not match line breaks by default):



'(?s)(?=(?:.{5})+$)'






share|improve this answer












share|improve this answer



share|improve this answer










answered Nov 16 '18 at 12:17









Wiktor StribiżewWiktor Stribiżew

329k16149228




329k16149228








  • 1





    @AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:46











  • thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

    – Andre Elrico
    Nov 16 '18 at 12:49











  • @AndreElrico You may want to read my quantfier explanations, too.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:53
















  • 1





    @AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:46











  • thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

    – Andre Elrico
    Nov 16 '18 at 12:49











  • @AndreElrico You may want to read my quantfier explanations, too.

    – Wiktor Stribiżew
    Nov 16 '18 at 12:53










1




1





@AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

– Wiktor Stribiżew
Nov 16 '18 at 12:46





@AndreElrico 1) It does not matter if you use lazy or greedy quantifiers here, (?=(?:.{5})+?$) = (?=(?:.{5})+$) because the next pattern is $, end of string and .{5} goes matching up to the end of the string anyway, 2) since the regex searches for matches from left to right, the 2nd position is matched, not the 5 from the end. PCRE regex cannot be set to search from the end.

– Wiktor Stribiżew
Nov 16 '18 at 12:46













thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

– Andre Elrico
Nov 16 '18 at 12:49





thanks you also found this here rexegg.com/regex-quantifiers.html#longest_shortest . this was a missing piece in my brain

– Andre Elrico
Nov 16 '18 at 12:49













@AndreElrico You may want to read my quantfier explanations, too.

– Wiktor Stribiżew
Nov 16 '18 at 12:53







@AndreElrico You may want to read my quantfier explanations, too.

– Wiktor Stribiżew
Nov 16 '18 at 12:53






















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