Add self-loops to a graph file : SCRIPT

script-graph-mtx-add-self-loop.js

const fs = require('fs');
const path = require('path');
const readline = require('readline');




// Read the header of a graph file.
async function readGraphHeader(pth) {
  var fstream = fs.createReadStream(pth);
  var rl = readline.createInterface({input: fstream, crlfDelay: Infinity});
  for await (var ln of rl) {
    if (ln.startsWith('%')) continue;
    var [rows, cols, size] = ln.split(' ').map(parseFloat);
    rl.close();
    fstream.close();
    return {rows, cols, size};
  }
  rl.close();
  fstream.close();
  return {rows: 0, cols: 0, size: 0};
}

// Read the last n bytes of a file.
function readFileTail(pth, n) {
  var fd    = fs.openSync(pth, 'r');
  var stats = fs.fstatSync(fd);
  var buf   = Buffer.alloc(n);
  fs.readSync(fd, buf, 0, n, stats.size-n);
  fs.closeSync(fd);
  return buf.toString();
}


// Add self-loops to a graph file.
async function addSelfLoops(inp, out) {
  var {rows} = await readGraphHeader(inp);
  var tail   = readFileTail(inp, 2);
  fs.copyFileSync(inp, out);
  var fstream = fs.createWriteStream(out, {flags: 'a'});
  if (/\r$|\r?\n$/.test(tail)) fstream.write('\n');
  for (var i=0; i<rows; i++)
    fstream.write(`${i} ${i}\n`);
  fstream.end();
}