Read and Write CSV using fast-csv package in Node.js

Question

I am trying to write a simple node program that reads a csv file, extracts a column (say second) and writes it to another CSV file. I am reading the contents to an array and then writing that array to file.

Stages and data in each step

inputfile

123,456,789,abc
def,ghi,232,jkl

array

['456','ghi']

outputfile

4,5,6
g,h,i

output needed

456
ghi

Am i just missing a configuration or is the way i am writing data wrong? Is my block of code to write to file within END block not correct?

Here is my code

var fast_csv = require('fast-csv');
var tempArray=new Array();
console.log("START");
fast_csv.fromPath("inputfile.txt").on("data", function(data){
    tempArray.push(data[1]);  
})
  .on("end", function(){
    tempArray.sort();
    console.log(tempArray);

    fast_csv.writeToPath("outputfile.csv", tempArray)
   .on("finish", function(){
      console.log("END");
   });

});

any suggestions ?

Ninja
– Ninja

2016-10-09 03:52:53 +00:00
Commented Oct 9, 2016 at 3:52 — Ninja
– Ninja, Commented Oct 9, 2016 at 3:52
Their examples are trash

BitShift
– BitShift

2022-01-14 10:02:46 +00:00
Commented Jan 14, 2022 at 10:02 — BitShift
– BitShift, Commented Jan 14, 2022 at 10:02

Galivan · Accepted Answer · 2017-03-11 00:55:35Z

4

It treats each element in the array as an array, so '456' is treated as an array with the elements 4,5,6.

A strange workaround I did was to loop through the array and put each element inside its own array, so it would be:

var newArray = [];

 for( var i = 0; i < tempArray.length; i++){
 var arr = [];
 arr.push(tempArray[i]);
newArray.push(arr);
}

And then write the "newArray".

But otherwise if you write row by row, you can put each element inside a bracket, like:

var fast_csv = fastcsv.createWriteStream();
var writeStream = fs.createWriteStream("outputfile.csv");
fast_csv.pipe(writeStream);

for(var i = 0; i < tempArray.length; i++){
    fast_csv.write( [ tempArray[i]  ] );             //each element inside bracket
    }
fast_csv.end();

answered Mar 11, 2017 at 0:55

Galivan

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Comments

smg · Accepted Answer · 2017-03-11 01:15:53Z

1

Change: tempArray.push(data[1]); to: tempArray.push([data[1]]);

writeToPath takes an array of arrays.

Docs: https://www.npmjs.com/package/fast-csv

answered Mar 11, 2017 at 1:15

smg

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