计数值在R组内出现的次数

function countOccurrences(arr, target) {
    let count = 0;
    for (let i = 0; i < arr.length; i++) {
        if (arr[i] === target) {
            count++;
        }
    }
    return count;
}

const arr = [1, 2, 2, 3, 4, 2, 1];
const target = 2;
const occurrences = countOccurrences(arr, target);
console.log(`Number of occurrences of ${target}: ${occurrences}`);

import pandas as pd

data = {'A': [1, 2, 2, 3, 4, 2, 1]}
df = pd.DataFrame(data)

target = 2
occurrences = len(df[df['A'] == target])
print(f"Number of occurrences of {target}: {occurrences}")