score:4

Accepted answer

You can return 0 if the map index is equal to 1, or return the current element otherwise.

Example

const { useState } = React;

function App() {
  const [rowEdit, setRowEdit] = useState({
    rowEdit: { "1x0": [1, 1, 1, 1, 1] }
  });

  function onClick() {
    setRowEdit(prevState => ({
      ...prevState,
      rowEdit: {
        ...prevState.rowEdit,
        "1x0": prevState.rowEdit["1x0"].map((row, index) =>
          index === 1 ? 0 : row
        )
      }
    }));
  }

  return (
    <div>
      <button onClick={onClick}>update row</button>
      <div>{JSON.stringify(rowEdit)}</div>
    </div>
  );
}

ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>

<div id="root"></div>

score:1

It's unclear if you want to do this for all keys in the object, but I'm going to assume you do:

setRowEdit(rows => Object.entries(rows).reduce((obj, [rowId, row]) => ({
  ...obj,
  [rowId]: row.map((col, i) => i === 1 ? 0 : col),
}), {}));

Otherwise:

setRowEdit(rows => ({
  ...rows,
  '1x0': rows['1x0'].map((col, i) => i === 1 ? 0 : col),
}), {}));

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