javascript - (JS) 迭代后从 csv 中删除行

Question

我希望您能够帮助我在每次脚本迭代该行后从 csv 文件中删除该行？下面的代码可以很好地迭代 CSV 并在每行的基础上执行一个函数(这是选择将所有数据加载到数组中以提高速度)，但我想然后删除顶部条目 -刚刚使用过的一个 - 来自 csv。目的是让运行程序即使崩溃也能够持续调用任务:

fs = require('fs');

function readCsv(filename) {
    file = fs.open(filename, 'r');
    line = file.readLine();
        var next = function() {
            line = file.readLine();
            task(line, next)
        };
    task(line, next);

function task(data, callback) {
    // Thing to do with data
}

Answer 1

像这样使用 Stream 应该可以工作。

const Transform = require('stream').Transform;
const util = require('util');
const Readable = require('stream').Readable;
const fs = require('fs');


class ProcessFirstLine extends Transform {
    constructor(args) {
        super(args);
        this._buff = '';
    }

    _transform(chunk, encoding, done) {

            // collect string into buffer
            this._buff += chunk.toString();

            // Create array of lines
            var arr = this._buff
                        .trim() // Remove empty lines at beginning and end of file
                        .split(/\n/), // Split lines into an array
                len = arr.length; // Get array length


            if(len > 0) {

                // Loop through array and process each line
                for(let i = 0; i < len; i++) {

                    // Grab first element from array
                    let line = arr.shift();

                    // Process the line
                    this.doSomethingWithLine(line);

                }

                // Push our array as a String (technically should be empty)
                this.push(arr.join(/\n/));

                // Empty the buffer
                this._buff = null;
            }

        done();
    }

    doSomethingWithLine(line) {
        console.log("doSomething:"+line);
    }
}

var input = fs.createReadStream('test.txt'); // read file
var output = fs.createWriteStream('test_.txt'); // write file

input
    .pipe(new ProcessFirstLine()) // pipe through line remover
    .pipe(output); // save to file