Calculate number of a letter in a string using Dart
سؤال
I try to calculate how many letter "a" i have in the sentence: "Hello Jordania".
I find the function contains. I using it like this:
var phrase = "Hello Jordania;
var comptenbrdea = phrase.contains('a');
print(comptenbrdea);
I get "True" as response. Normal you will say, I know, but I dont find the right function to calculate how many time i get an a. I can maybe do something with a loop if I can check every single character? ... I'm lost on http://www.dartlang.org/search.html?cx=011220921317074318178%3Ai4mscbaxtru&ie=UTF-8&hl=en&q=string_scanner ... Can some one help me ?
المحلول
Here's a simple way to do it:
void main() {
print('a'.allMatches('Hello Jordania').length); // 2
}
Edit: the tested string is the parameter, not the character to be counted.
نصائح أخرى
void main() {
const regExp = const RegExp("a");
print(regExp.allMatches("Hello Jordania").length); // 2
}
You need to iterate on the characters and count them, you comment above contains a general function for building a histogram, but the version that just counts 'a's is probably good for you to write. I'll just show you how to loop over characters:
var myString = "hello";
for (var char in myString.splitChars()) {
// do something
}
void main(){
String str = "yours string";
Map<String, int> map = {};
for(int i = 0; i < str.length; i++){
int count = map[str[i]] ?? 0;
map[str[i]] = count + 1;
}
print(map);
}
// count letters
Map<int,int> counts = new Map<int,int>();
for (var c in s.charCodes() ) {
counts[c] = counts.putIfAbsent(c, p()=>0) + 1;
}
// print counts
for (var c in counts.getKeys())
print("letter ${new String.fromCharCodes([c])} count=${counts[c]}");
Probably not the best one, but you can also do something like this.
void main() {
var a = "ht://adfd//.coma/";
int count = a.split("t").length - 1;
print(count);
}
You will need to subtract 1 because it is splitting into a list first and then counting the size of that list.