'columns' unparse config not working when first object doesn't have all properties

[TheSlimvReal]

When using the columns unparse config option together with a data array where the first object does not have all properties that are listed in the columns array, then not all columns of the columns array are used even if later objects have these values.

E.g.

const columns= ["First", "Second", "Third"];
const rows= [
  { First: "1-1"},
  {
    First: "2-1",
    Second: "2-2",
    "Third": "2-3",
  },
];
const result = Papa.unparse(
  { data: rows},
  {
    header: true,
    columns: columns,
  }
);
console.log(result)

The result is

First
1-1
2-1

instead of the expected

First,Second,Third
1-1,,
2-1,2-2,2-3

[pokoli]

I guess the problem is that the columns array is modified on the first colum when it should not be.
Could you please upload a PR to fix it which includes a minimum test case (your example sounds like a good solution)

[TheSlimvReal]

Thanks for the quick response. I will try to make the PR. As this would be my first contribution to Papaparse, do you @pokoli have some pointers for me where I would have to look for a solution/implement the tests and the code?

[pokoli]

@TheSlimvReal That will be great.
THinks to note:

• You do not need to update the minified file as this will be done by the release process.
• There are already tests for unparse, make sure to add yours at the end (feel free to use them as reference).
• Feel free to ask any other doubts you may have ;-)

[TheSlimvReal]

After going through the tests cases I found this one:

{
  description: "Column option used to manually specify keys",
  notes: "...",
  input: [{a: 1, b: '2'}, {}, {a: 3, d: 'd', c: 4,}],
  config: {columns: ['a', 'b', 'c']},
  expected: 'a,b,c\r\n1,2,\r\n\r\n3,,4'
},

Which made me realize that with

...
const result = Papa.unparse(
  rows,   // <-- pass the data object directly instead of { data: rows }
  {
    header: true,
    columns: columns,
  }
);
...

My above example works.

Therefore my question @pokoli: Is it a bug that it does not work when passing an object instead of an array or is this behavior intended?

[TheSlimvReal]

anyway I created a PR that resolves the issue #919

[TheSlimvReal]

Generally, I am wondering whether the options columns and fields are not the same thing and columns could therefore be removed?