Can anyone provide guidance on how to iterate through this array and retrieve every second "note" starting at a specific note, for example starting at F and getting f,a,c? Your help is much appreciated :)
let notes = ['c','d','e','f','g','a','b'];
Can anyone provide guidance on how to iterate through this array and retrieve every second "note" starting at a specific note, for example starting at F and getting f,a,c? Your help is much appreciated :)
let notes = ['c','d','e','f','g','a','b'];
You can implement findIndex and filter using the remainder operator in your code
Assuming you are looking for a circular wraparound
When wrapping around, I get f, a, c, e. If not wrapping, I get f, a. Did you mean to include the letter e in your expected output?
let notes = ['c', 'd', 'e', 'f', 'g', 'a', 'b'];
const findNotes = (startNote, gap) => {
const start = notes.findIndex(note => note === startNote)
if (start !=-1) return notes.slice(start).concat(notes.slice(0,start)).filter((note, i) => i % gap === 0)
return "not found"
};
console.log(findNotes("f", 2))To streamline this process, you can associate each note with a specific index and then duplicate the notes array to facilitate accessing values in a round-robin fashion.
let notes = ['c', 'd', 'e', 'f', 'g', 'a', 'b'],
indexMap = notes.reduce((map, n, i) => map.set(n, i), new Map),
twoNotes = [...notes, ...notes]
Next, define a function that retrieves the initial index from the mapping and returns the items at the next 2 indices.
function findNext(note) {
const index = indexMap.get(note)
return [twoNotes[index], twoNotes[index+2], twoNotes[index+4]]
}
Alternatively, for more flexibility in selecting future indices, a generic function can be created to accept the indices array as an argument.
function findNext(note) {
const index = indexMap.get(note)
return [0, 2, 4].map(i => twoNotes[i + index])
}
let notes = ['c', 'd', 'e', 'f', 'g', 'a', 'b'],
indexMap = notes.reduce((map, n, i) => map.set(n, i), new Map),
twoNotes = [...notes, ...notes]
function findNext(note) {
const index = indexMap.get(note)
return [0, 2, 4].map(i => twoNotes[i + index])
}
console.log(...findNext('f'))
console.log(...findNext('c'))If you want your index variable to reset to 0 once it reaches the end of the notes array, you can achieve this using the modulo operator. This will give you the output f,a,c,:
let notes = ['c','d','e','f','g','a','b'];
let startIndex = notes.indexOf('f');
for (let i = startIndex; i !== startIndex-1; i = (i + 2) % notes.length)) {
document.write(notes[i]+",");
}
For even better performance in certain cases, there is an alternative method you can use with the for loop...
let notes = ['c','d','e','f','g','a','b'];
let startIndex = notes.indexOf('f')-2;
for (
let i = startIndex;
i !== startIndex-1;
(i = (i + 2) % notes.length)==document.write(notes[i]+",")
);
Remember: don't forget the ';' after the for loop if you're not using '{}'.
Another approach would be to rearrange the array by slicing and then iterating through it:
let notes = ['c','d','e','f','g','a','b'];
let startIndex = notes.indexOf('f');
notes = [
...notes.slice(startIndex),
...notes.slice(0, startIndex)
];
for (let i = 0; i < notes.length - 2; i += 2) {
let note = notes[i];
document.write(note+",");
}
To extract specific elements from an array starting at a certain index, you can use a for loop and specify the starting index. For instance, executing the following code will result in: 'f', 'a'.
let notes = ['c', 'd', 'e', 'f', 'g', 'a', 'b'];
let startIndex = 3; // start at 'f'
for (let i = startIndex; i < notes.length; i += 2) {
let note = notes[i];
console.log(note);
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