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String related infix operators

Source: vignettes/articles/e_strings_inops.Rmd
e_strings_inops.Rmd
library(tinycodet)
#> Run `?tinycodet::tinycodet` to open the introduction help page of 'tinycodet'.

 

Overview

‘tinycodet’ adds 3 sets of string-related operators.

First, sub-setting operators:

  • x %s><% ss: returns the first n1 and last n2 characters from each string in character vector x.
  • x %s<>% ss trims away first n1 and last n2 characters from each string in character vector x.

Second, ‘stringi’ already has the %s+%, %s*%, and %s$% operators, and ‘tinycodet’ adds some additional string arithmetic operators to complete the set:

  • x %s-% p removes pattern p from each string in character vector x;
  • x %s/% p counts how often pattern p occurs in each string of character vector x.
  • x %s//% brk counts how often the text boundary specified in list brk occurs in each string of character vector x.
  • x %ss% p splits the strings in x by a delimiter character/pattern defined in p, and removes p in the process.

And finally, string search operators:

  • x %s{}% p operator checks for every string in character vector x if the pattern defined in p is present. Can also be used to check if the strings specifically start or end with pattern p.
  • x %s!{}% p operator checks for every string in character vector x if the pattern defined in p is not present. Can also be used to check if the strings specifically does not start or end with pattern p.
  • strfind()<- locates, extracts, or replaces found patterns.

 

The x %s-% p and x %s/% p operators, and the string detection operators (%s{}%, %s!{}%, strfind()<-) perform pattern matching for various purposes. When a character vector or string is given on the right hand side, this is interpreted as case-sensitive regex patterns from stringi.

But, of course, sometimes one wants to change this. For example, one may want it to be case insensitive. Or perhaps one wants to use fixed expressions, or something else.

Instead of giving a string or character vector of regex patterns, one can also supply a list to the right-hand side, to specify exactly how the pattern should be interpreted. The list should use the exact same naming convention as stringi. For example:

  • list(regex=p, case_insensitive=FALSE, ...)
  • list(fixed=p, ...)
  • list(coll=p, ...)
  • list(charclass=p, ...)

For convenience, ‘tinycodet’ adds the following functions for this purpose:

  • s_regex(p, ...) is equivalent to list(regex = p, ...)
  • s_fixed(p, ...) is equivalent to list(fixed = p, ...)
  • s_coll(p, ...) is equivalent to list(coll = p, ...)
  • s_chrcls(p, ...) is equivalent to list(charclass = p, ... )

The next sections will give more details on the given overview.

 

 

String subsetting operators

The x %s><% ss operator returns a subset of each string in character vector x. Here ss is a vector of length 2, or a matrix with nrow(ss)=length(x) and 2 columns. The object ss should consist entirely of non-negative integers (thus 0, 1, 2, etc. are valid, but -1, -2, -3 etc are not valid). The first element/column of ss gives the number of characters counting from the left side to be extracted from x. The second element/column of ss gives the number of characters counting from the right side to be extracted from x.

Here are 2 examples:

x <- c(paste0(letters[1:13], collapse=""), paste0(letters[14:26], collapse=""))
print(x)
#> [1] "abcdefghijklm" "nopqrstuvwxyz"
ss <- c(2,3)
x %s><% ss
#> [1] "abklm" "noxyz"

x <- c(paste0(letters[1:13], collapse=""), paste0(letters[14:26], collapse=""))
print(x)
#> [1] "abcdefghijklm" "nopqrstuvwxyz"
ss <- c(1,0)
x %s><% ss
#> [1] "a" "n"

Thus x %s><% ss “gets” or extracts the given number of characters from the left and the right, and removes the rest. There is also x %s<>% ss, which is the opposite: it trims away the number of characters from the left and right as defined in the matrix ss, leaving you with whatever is left.

Here are again 2 examples:

x <- c(paste0(letters[1:13], collapse=""), paste0(letters[14:26], collapse=""))
print(x)
#> [1] "abcdefghijklm" "nopqrstuvwxyz"
ss <- c(2,3)
x %s<>% ss
#> [1] "cdefghij" "pqrstuvw"

x <- c(paste0(letters[1:13], collapse=""), paste0(letters[14:26], collapse=""))
print(x)
#> [1] "abcdefghijklm" "nopqrstuvwxyz"
ss <- c(1,0)
x %s<>% ss
#> [1] "bcdefghijklm" "opqrstuvwxyz"

 

String arithmetic

The tinycodet package includes 7 string arithmetic operators (3 of which re-exported from ‘stringi’):

  • x %s+% y concatenates x and y (exported from ‘stringi’);
  • x %s-% p removes pattern p from each string in character vector x;
  • x %s*% n repeats each string in character vector x for n times (exported from ‘stringi’);
  • x %s/% p counts how often pattern p occurs in each string of character vector x.
  • x %s//% brk counts how often the text boundary specified in list brk occurs in each string of character vector x.
  • e1 %s$% e2 provides access to stri_sprintf (exported from ‘stringi’);
  • x %ss% p splits the strings in x by a delimiter character/pattern defined in p, and removes p in the process.

I.e.:

"Hello "%s+% " world"
#> [1] "Hello  world"
c("Hello world", "Goodbye world") %s-% " world"
#> [1] "Hello"   "Goodbye"
c("Hello world", "Goodbye world") %s-% s_fixed(" world")
#> [1] "Hello"   "Goodbye"
c("Ha", "Ho", "Hi", "Hu", "He", "Ha") %s*% 2:7
#> [1] "HaHa"           "HoHoHo"         "HiHiHiHi"       "HuHuHuHuHu"    
#> [5] "HeHeHeHeHeHe"   "HaHaHaHaHaHaHa"
c("hello World & goodbye world", "world domination!") %s/% s_fixed("world", case_insensitive = TRUE)
#> [1] 2 1
c("hello world & goodbye world", "world domination!") %s//% list(type = "word")
#> [1] 9 4

The right-side arguments y, and n can be a single value, or a vector of the same length as x. The right-side argument p can be string or character vector, or a list as described in the Overview section.

 

Detect Patterns

Detect

The x %s{}% p operator checks for every string in character vector x if the pattern defined in p is present. The x %s!{}% p operator checks for every string in character vector x if the pattern defined in p is NOT present.

Examples:

x <- c(paste0(letters[1:13], collapse=""), paste0(letters[14:26], collapse=""))
print(x)
#> [1] "abcdefghijklm" "nopqrstuvwxyz"
x %s{}% "a"
#> [1]  TRUE FALSE
x %s!{}% "a"
#> [1] FALSE  TRUE
which(x %s{}% "a")
#> [1] 1
which(x %s!{}% "a")
#> [1] 2
x[x %s{}% "a"]
#> [1] "abcdefghijklm"
x[x %s!{}% "a"]
#> [1] "nopqrstuvwxyz"

Detect - start or end with pattern

When supplying a list on the right hand side (see the Overview section above), one can include the list element at = "start" or at = "end":

Examples:


x <- c(paste0(letters, collapse=""), paste0(rev(letters), collapse=""), NA)
p <- s_fixed("abc", at = "start")
x %s{}% p
#> [1]  TRUE FALSE    NA
stringi::stri_startswith(x, fixed = "abc") # same as above
#> [1]  TRUE FALSE    NA

p <- s_fixed("xyz", at = "end")
x %s{}% p
#> [1]  TRUE FALSE    NA
stringi::stri_endswith(x, fixed = "xyz") # same as above
#> [1]  TRUE FALSE    NA

p <- s_fixed("cba", at = "end")
x %s{}% p
#> [1] FALSE  TRUE    NA
stringi::stri_endswith(x, fixed = "cba") # same as above
#> [1] FALSE  TRUE    NA

p <- s_fixed("zyx", at = "start")
x %s{}% p
#> [1] FALSE  TRUE    NA
stringi::stri_startswith(x, fixed = "zyx") # same as above
#> [1] FALSE  TRUE    NA

 

Locate, Extract, or Replace Patterns

strfind()<- locates, extracts, or replaces found patterns. Like the other operators, the argument p can be a string or character vector, or a list as described in the Overview section above.

It can be used in several different ways.

 

Extract

strfind() finds all pattern matches, and returns the extractions of the findings in a list, just like stringi::stri_extract_all():

x <- rep('The quick brown fox jumped over the lazy dog.', 3)
p <- s_fixed(c('quick', 'brown', 'fox'))
strfind(x, p)
#> [[1]]
#> [1] "quick"
#> 
#> [[2]]
#> [1] "brown"
#> 
#> [[3]]
#> [1] "fox"

 

Locate

strfind(..., i = "all" ), finds all pattern matches like stringi::stri_locate_all(). And strfind(..., i = i), where i is an integer vector, locates the ith occurrence of a pattern, and reports the locations in a matrix, just like stri_locate_ith():

p <- s_fixed("the", case_insensitive = TRUE)
strfind(x, p, i = "all")
#> [[1]]
#>      start end
#> [1,]     1   3
#> [2,]    33  35
#> 
#> [[2]]
#>      start end
#> [1,]     1   3
#> [2,]    33  35
#> 
#> [[3]]
#>      start end
#> [1,]     1   3
#> [2,]    33  35
strfind(x, p, i = c(1, -1, 2))
#>      start end
#> [1,]     1   3
#> [2,]    33  35
#> [3,]    33  35

 

Replace

strfind() <- value finds pattern matches in variable x, replaces the pattern matches with the character vector specified in value, and assigns the transformed character vector back to x. This is somewhat similar to stringi::stri_replace(), though the replacement is done in-place. It supports vectorized, dictionary, first, and last replacement:

# vectorized replacement:
x <- rep('The quick brown fox jumped over the lazy dog.', 3)
p <- c('quick', 'brown', 'fox')
rp <- c('SLOW',  'BLACK', 'BEAR')
strfind(x, p) <- rp
print(x)
#> [1] "The SLOW brown fox jumped over the lazy dog."  
#> [2] "The quick BLACK fox jumped over the lazy dog." 
#> [3] "The quick brown BEAR jumped over the lazy dog."

# dictionary replacement:
# quick => SLOW; brown => BLACK; fox => BEAR
x <- rep('The quick brown fox jumped over the lazy dog.', 3)
p <- c('quick', 'brown', 'fox')
rp <- c('SLOW',  'BLACK', 'BEAR')
strfind(x, p, rt = "dict") <- rp
print(x)
#> [1] "The SLOW BLACK BEAR jumped over the lazy dog."
#> [2] "The SLOW BLACK BEAR jumped over the lazy dog."
#> [3] "The SLOW BLACK BEAR jumped over the lazy dog."

# first replacement:
x <- rep('The quick brown fox jumped over the lazy dog.', 3)
p <- s_fixed("the", case_insensitive = TRUE)
rp <- c('ONE')
strfind(x, p, rt = "first") <- rp
print(x)
#> [1] "ONE quick brown fox jumped over the lazy dog."
#> [2] "ONE quick brown fox jumped over the lazy dog."
#> [3] "ONE quick brown fox jumped over the lazy dog."

# last replacement:
x <- rep('The quick brown fox jumped over the lazy dog.', 3)
p <- s_fixed("the", case_insensitive = TRUE)
rp <- c('ONE')
strfind(x, p, rt = "last") <- rp
print(x)
#> [1] "The quick brown fox jumped over ONE lazy dog."
#> [2] "The quick brown fox jumped over ONE lazy dog."
#> [3] "The quick brown fox jumped over ONE lazy dog."