EN
JavaScript - remove duplicated lines
8
points
In this short article, we would like to show how to remove duplicated lines from some text using JavaScript.
Quick solution:
// ONLINE-RUNNER:browser;
const newLineExpression = /\r\n|\n\r|\n|\r/g;
const removeDuplicatedLines = (text) => {
let result = '';
const blocker = {}; // prevents lines dupplication
const lines = text.split(newLineExpression);
for (const line of lines) {
if (blocker.hasOwnProperty(line)) {
continue;
}
blocker[line] = true;
result += line + '\n';
}
return result;
};
// Usage example:
const text = `a
b
b
a
a
c
c`;
console.log(removeDuplicatedLines(text)); // a
// b
// c
filter() based example
This approach uses a functional programming pattern.
// ONLINE-RUNNER:browser;
const newLineExpression = /\r\n|\n\r|\n|\r/g;
const removeDuplicatedLines = (text) => {
return text.split(newLineExpression)
.filter((item, index, array) => array.indexOf(item) === index)
.join('\n');
};
// Usage example:
const text = `a
b
b
a
a
c
c`;
console.log(removeDuplicatedLines(text)); // a
// b
// c
reduce() based example
This approach was created to show that it is possible to get the same effect with reduce() method.
// ONLINE-RUNNER:browser;
const newLineExpression = /\r\n|\n\r|\n|\r/g;
const removeDuplicatedLines = (text) => {
const blocker = {}; // prevents lines dupplication
return text.split(newLineExpression)
.reduce((result, line) => {
if (blocker.hasOwnProperty(line)) {
return result;
}
blocker[line] = true;
return result + line + '\n';
}, '');
};
// Usage example:
const text = `a
b
b
a
a
c
c`;
console.log(removeDuplicatedLines(text)); // a
// b
// c