How to update with React Hooks specific value of an array inside an object?

Question

I have an object which i want to update it using React Hooks

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

I loop through the array with .map, so i have the index for each element. How can i make the second value equal to 0?

Answer 1

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> 

Answer 2

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),
}), {}));