Find the nth occurrence of a specific character in a String

albobz

I am trying to write a function that returns the integer index value for the nth occurrence of a specified character c, like:

int findNthChar(String a, char c, int n)

I know to use a while loop but am not too sure of the code within it.

GoToLoop

1. https://Processing.org/reference/String_indexOf_.html
2. http://Docs.Oracle.com/javase/8/docs/api/java/lang/String.html#indexOf-int-int-

/** 
 * Nth Char in Str (v1.1)
 * GoToLoop (2017/Jul/25)
 *
 * Forum.Processing.org/two/discussion/23582/
 * find-the-nth-occurrence-of-a-specific-character-in-a-string#Item_1
 */

static final String TEST = "Find the nth occurr specific char in a String.";
static final char CH = 'n';
static final int NTH = 3;

void setup() {
  println(TEST);
  print("Len: " + TEST.length());
  println(" \tChar: " + CH + " \tNth: " + NTH);
  println("Index: " + findIdxOfNthChar(TEST, CH, NTH));
  exit();
}

static final int findIdxOfNthChar(final String s, final char ch, final int n) {
  int i = 0, idx = -1;
  while (i++ < n)  if ((idx = s.indexOf(ch, idx + 1)) < 0)  return -1;
  return idx;
}

albobz

Similar to this I also need to count how many times a specific character occurs in a String. Do I just need to remove the while statement or is there more to it?

GoToLoop

/** 
 * Nth Char in Str (v2.1)
 * GoToLoop (2017/Jul/26)
 *
 * Forum.Processing.org/two/discussion/23582/
 * find-the-nth-occurrence-of-a-specific-character-in-a-string#Item_3
 */

static final String TEST = "Find the nth occurr specific char in a String.";
static final char CH = 'n';
static final int NTH = 3;

void setup() {
  println(TEST);
  print("Len: " + TEST.length());
  println(" \tChar: " + CH + " \tNth: " + NTH);
  print("Index: " + findIdxOfNthChar(TEST, CH, NTH));
  println(" \tFound: " + findCharOccurs(TEST, CH));
  exit();
}

static final int findIdxOfNthChar(final String s, final char ch, final int n) {
  int i = 0, idx = -1;
  while (i++ < n)  if ((idx = s.indexOf(ch, idx + 1)) < 0)  return -1;
  return idx;
}

static final int findCharOccurs(final String s, final char ch) {
  int n = 0, idx = -1;
  while ((idx = s.indexOf(ch, idx + 1)) >= 0)  ++n;
  return n;
}

albobz

I now have to utilize the findNthChar():

/********************
*  Searches thtrough the string, locates the nth term of the character c. and returns
*  the index of that character, using a while loop that starts at the beginning of the
*  String and scans forward.
********************/
int findNthChar(String a, char c, int n)
{
  int w = 0; //intial value for while loop
  int idx = -1; //initial index value
  while (w++ < n)
  {
    if ((idx = a.indexOf(c, idx+1)) < 0)
    {
      return -1;
    }
  }
  return idx;
}

and the stringFront():

/********************
*  Returns the first count characters of the String as a new String.
********************/
String stringFront(String s, int count)
{
  String ss = s.substring(0,count);
  return ss;
}

to create the getFirstWords():

/********************
*  Returns a new String containing the first n words in s, where the character delimiter
*  defines a word boundary, using stringFront to get the actual words as a new String.
********************/
String getFirstWords(String s, int n, char delimiter)
{
  String firstWord = stringFront(s, findNthChar(s, delimiter, n));
  return firstWord;
}

Am I close with getFirstWords()?

Chrisir

I don't think so.

Returns a new String containing the first n words in s

words is plural

GoToLoop

/** 
 * Nth Char in Str (v3.1)
 * GoToLoop (2017/Jul/26)
 *
 * Forum.Processing.org/two/discussion/23582/
 * find-the-nth-occurrence-of-a-specific-character-in-a-string#Item_6
 */

static final String TEST = "Find the nth occurr specific char in a String.";
static final char CH = 'n';
static final int NTH = 3, WORDS = 4;

void setup() {
  println(TEST);
  print("Len: " + TEST.length());
  println(" \tChar: " + CH + " \tNth: " + NTH);
  print("Index: " + findIdxOfNthChar(TEST, CH, NTH));
  println(" \tFound: " + findCharOccurs(TEST, CH) + ENTER);

  print("Words Total: " + getNumberOfWords(TEST, ' '));
  println(" \tWords Requested: " + WORDS);
  println("Words: " + getFirstWords(TEST, ' ', WORDS));

  exit();
}

static final int findIdxOfNthChar(final String s, final char ch, final int n) {
  int i = 0, idx = -1;
  while (i++ < n)  if ((idx = s.indexOf(ch, idx + 1)) < 0)  return -1;
  return idx;
}

static final int findCharOccurs(final String s, final char ch) {
  int n = 0, idx = -1;
  while ((idx = s.indexOf(ch, idx + 1)) >= 0)  ++n;
  return n;
}

static final String stringFront(final String s, final int n) {
  return s.substring(0, n);
}

static final int getNumberOfWords(final String s, final char ch) {
  return split(s, ch).length;
}

static final String getFirstWords(final String s, final char ch, final int n) {
  final String[] found  = split(s, ch);
  final int number = min(abs(n), found.length);
  final String[] firsts = subset(found, 0, number);
  return join(firsts, ch);
}