implemented count function

doc/specs/stdlib_strings.md

@@ -280,7 +280,7 @@ end program demo_slice
 Returns the starting index of the `occurrence`th occurrence of the substring `pattern` 
 in the input string `string`.  
 Default value of `occurrence` is set to `1`. 
-If `consider_overlapping` is not provided or is set to `.true.` the function counts two overlapping occurrences of substring as two different occurrences.  
+If `consider_overlapping` is not provided or is set to `.true.` the function counts two overlapping occurrences of substring `pattern` as two different occurrences.  
 If `occurrence`th occurrence is not found, function returns `0`.
 
 #### Syntax
@@ -308,7 +308,7 @@ Elemental function
 
 #### Result value
 
-The result is a scalar of integer type or integer array of rank equal to the highest rank among all dummy arguments.
+The result is a scalar of integer type or an integer array of rank equal to the highest rank among all dummy arguments.
 
 #### Example
 
@@ -381,4 +381,56 @@ program demo_replace_all
   ! string <-- "technology here, technology there, technology everywhere"
 
 end program demo_replace_all
-```
+```
+
+
+<!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
+### `count`
+
+#### Description
+
+Returns the number of times substring `pattern` has occurred in the input string `string`.  
+If `consider_overlapping` is not provided or is set to `.true.` the function counts two overlapping occurrences of substring `pattern` as two different occurrences.
+
+#### Syntax
+
+`string = [[stdlib_strings(module):count(interface)]] (string, pattern [, consider_overlapping])`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Elemental function
+
+#### Argument
+
+- `string`: Character scalar or [[stdlib_string_type(module):string_type(type)]].
+  This argument is intent(in).
+- `pattern`: Character scalar or [[stdlib_string_type(module):string_type(type)]].
+  This argument is intent(in).
+- `consider_overlapping`: logical.
+  This argument is intent(in) and optional.
+
+#### Result value
+
+The result is a scalar of integer type or an integer array of rank equal to the highest rank among all dummy arguments.
+
+#### Example
+
+```fortran
+program demo_count
+  use stdlib_string_type, only: string_type, assignment(=)
+  use stdlib_strings, only : count
+  implicit none
+  type(string_type) :: string
+
+  string = "How much wood would a woodchuck chuck if a woodchuck could chuck wood?"
+
+  print *, count(string, "wood")                                  ! 4
+  print *, count(string, ["would", "chuck", "could"])             ! [1, 4, 1]
+  print *, count("a long queueueueue", "ueu", [.false., .true.])  ! [2, 4]
+
+end program demo_count
+```

src/stdlib_strings.f90

@@ -12,7 +12,7 @@ module stdlib_strings
 
     public :: strip, chomp
     public :: starts_with, ends_with
-    public :: slice, find, replace_all
+    public :: slice, find, replace_all, count
 
 
     !> Remove leading and trailing whitespace characters.
@@ -93,6 +93,17 @@ module stdlib_strings
         module procedure :: replace_all_char_char_char
     end interface replace_all
 
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> [Specifications](../page/specs/stdlib_strings.html#count)
+    !> Version: experimental
+    interface count
+        module procedure :: count_string_string
+        module procedure :: count_string_char
+        module procedure :: count_char_string
+        module procedure :: count_char_char
+    end interface count
+
 contains
 
 
@@ -649,4 +660,87 @@ pure function replace_all_char_char_char(string, pattern, replacement) result(re
 
     end function replace_all_char_char_char
 
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_string_string(string, pattern, consider_overlapping) result(res)
+        type(string_type), intent(in) :: string
+        type(string_type), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(char(string), char(pattern), consider_overlapping)
+
+    end function count_string_string
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_string_char(string, pattern, consider_overlapping) result(res)
+        type(string_type), intent(in) :: string
+        character(len=*), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(char(string), pattern, consider_overlapping)
+
+    end function count_string_char
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_char_string(string, pattern, consider_overlapping) result(res)
+        character(len=*), intent(in) :: string
+        type(string_type), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(string, char(pattern), consider_overlapping)
+
+    end function count_char_string
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_char_char(string, pattern, consider_overlapping) result(res)
+        character(len=*), intent(in) :: string
+        character(len=*), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: lps_array(len(pattern))
+        integer :: res, s_i, p_i, length_string, length_pattern
+        logical :: consider_overlapping_
+
+        consider_overlapping_ = optval(consider_overlapping, .true.)
+        res = 0
+        length_string = len(string)
+        length_pattern = len(pattern)
+
+        if (length_pattern > 0 .and. length_pattern <= length_string) then
+            lps_array = compute_lps(pattern)
+
+            s_i = 1
+            p_i = 1
+            do while(s_i <= length_string)
+                if (string(s_i:s_i) == pattern(p_i:p_i)) then
+                    if (p_i == length_pattern) then
+                        res = res + 1
+                        if (consider_overlapping_) then
+                            p_i = lps_array(p_i)
+                        else
+                            p_i = 0
+                        end if
+                    end if
+                    s_i = s_i + 1
+                    p_i = p_i + 1
+                else if (p_i > 1) then
+                    p_i = lps_array(p_i - 1) + 1
+                else
+                    s_i = s_i + 1
+                end if
+            end do
+        end if
+
+    end function count_char_char
+
+
 end module stdlib_strings

src/tests/string/test_string_functions.f90

@@ -4,7 +4,7 @@ module test_string_functions
     use stdlib_error, only : check
     use stdlib_string_type, only : string_type, assignment(=), operator(==), &
                                     to_lower, to_upper, to_title, to_sentence, reverse
-    use stdlib_strings, only: slice, find, replace_all                                   
+    use stdlib_strings, only: slice, find, replace_all, count
     use stdlib_optval, only: optval
     use stdlib_ascii, only : to_string
     implicit none
@@ -378,6 +378,49 @@ subroutine test_replace_all
 
     end subroutine test_replace_all
 
+    subroutine test_count
+        type(string_type) :: test_string_1, test_string_2, test_pattern_1, test_pattern_2
+        test_string_1 = "DNA sequence: AGAGAGAGTCCTGTCGAGA"
+        test_string_2 = "DNA sequence: GTCCTGTCCTGTCAGA"
+        test_pattern_1 = "AGA"
+        test_pattern_2 = "GTCCTGTC"
+
+        ! all 2 as string_type
+          call check(all(count([test_string_1, test_string_2], test_pattern_1) == [4, 1]), &
+                & 'count: all 2 as string_type, test case 1')
+          call check(all(count(test_string_1, [test_pattern_1, test_pattern_2], .false.) == [3, 1]), &
+                & 'count: all 2 as string_type, test case 2')
+          call check(count(test_string_2, test_pattern_1, .false.) == 1, &
+                & 'count: all 2 as string_type, test case 3')
+          call check(all(count([test_string_2, test_string_2, test_string_1], [test_pattern_2, &
+                & test_pattern_2, test_pattern_1], [.true., .false., .false.]) == [2, 1, 3]), &
+                & 'count: all 2 as string_type, test case 4')
+          call check(all(count([[test_string_1, test_string_2], [test_string_1, test_string_2]], [[test_pattern_1, &
+                & test_pattern_2], [test_pattern_2, test_pattern_1]], .true.) == [[4, 2], [1, 1]]), &
+                & 'count: all 2 as string_type, test case 5')
+
+        ! 1 string_type and 1 character scalar
+          call check(all(count(test_string_1, ["AGA", "GTC"], [.true., .false.]) == [4, 2]), &
+                & 'count: 1 string_type and 1 character scalar, test case 1')
+          call check(all(count([test_string_1, test_string_2], ["CTC", "GTC"], [.true., .false.]) &
+                & == [0, 3]), 'count: 1 string_type and 1 character scalar, test case 2')
+          call check(all(count(["AGAGAGAGTCCTGTCGAGA", "AGAGAGAGTCCTGTCGAGA"], test_pattern_1, &
+                & [.false., .true.]) == [3, 4]), &
+                & 'count: 1 string_type and 1 character scalar, test case 3')
+          call check(count(test_string_1, "GAG") == 4, &
+                & 'count: 1 string_type and 1 character scalar, test case 4')
+          call check(count("DNA sequence: GTCCTGTCCTGTCAGA", test_pattern_2, .false.) == 1, &
+                & 'count: 1 string_type and 1 character scalar, test case 5')
+
+        ! all 2 character scalar
+          call check(all(count("", ["mango", "trees"], .true.) == [0, 0]), &
+                & 'count: all 2 character scalar, test case 1')
+          call check(count("", "", .true.) == 0, 'count: all 2 character scalar, test case 2')
+          call check(all(count(["mango", "trees"], "", .true.) == [0, 0]), &
+                & 'count: all 2 character scalar, test case 3')
+
+    end subroutine test_count
+
 end module test_string_functions
 
 
@@ -394,5 +437,6 @@ program tester
     call test_slice_gen
     call test_find
     call test_replace_all
+    call test_count
 
 end program tester