Develop Reference

Merge neighbouring HTML table cells with same value using JS

I've been wrestling with this for a while. I have a table which is automatically generated based on some JSON data, which may vary. I'd like to merge neighbouring cells in the first column which have the same value, e.g. "fish" and "bird" in this table:
<table>
<tr>
<td>fish</td>
<td>salmon</td>
</tr>
<tr>
<td>fish</td>
<td>cod</td>
</tr>
<tr>
<td>fish</td>
<td>plaice</td>
</tr>
<tr>
<td>bird</td>
<td>robin</td>
</tr>
<tr>
<td>bird</td>
<td>crow</td>
</tr>
</table>
I don't want to use any libraries ideally, just pure JS.
This is what I would like it to look like:
table, tr, td {
border: solid 1px black;
}
<table>
<tr>
<td rowspan="3">fish</td>
<td>salmon</td>
</tr>
<tr>
<td>cod</td>
</tr>
<tr>
<td>plaice</td>
</tr>
<tr>
<td rowspan="2">bird</td>
<td>robin</td>
</tr>
<tr>
<td>crow</td>
</tr>
</table>
I've been finding different ways to identify the different values and their frequency and then change the rowspan to the right number and subsequently deleting the the other cells but these all broke down in differing use cases.
This is what I have so far:
let table = document.querySelector('table');
let rowCount = 1;
for (let i = 0; i < (table.rows.length - 1); i++) {
if (table.rows[i].cells[0].innerHTML === table.rows[i + 1].cells[0].innerHTML) {
rowCount++;
} else if (rowCount !== 1) {
table.rows[i].cells[0].setAttribute('rowspan', rowCount);
for (let j = (i - rowCount + 1); j < rowCount; j++) {
table.rows[j].cells[0].remove();
};
rowCount = 1;
};
};
table, tr, td {
border: solid 1px black;
}
<table>
<tr>
<td>fish</td>
<td>salmon</td>
</tr>
<tr>
<td>fish</td>
<td>cod</td>
</tr>
<tr>
<td>fish</td>
<td>plaice</td>
</tr>
<tr>
<td>bird</td>
<td>robin</td>
</tr>
<tr>
<td>bird</td>
<td>crow</td>
</tr>
</table>
This isn't doing what I want at all but I feel I'm really close! It's trying to count the number of (first column) cells for which the one below has the same value, assigning this number to the rowspan of the last relevant cell and then deleting the subsequent cells before looping back to catch the rest of them. I'd love for my final code to be a variation of this, so can someone show me where I'm going wrong please?

You were indeed pretty close!
A way to simplify quite a bit is to keep a reference to the current "header" cell, i.e. the one you want to increase the rowspan of. That way you don't have to deal with indexes at all, yielding a very straightforward algorithm:
For each row
Set firstCell to the row's first cell
If this is the first row OR firstCell's text is different from headerCell's text
Set headerCell to firstCell
Otherwise
Increase headerCell's rowSpan by 1
Remove firstCell
In JavaScript, it looks like this:
const table = document.querySelector('table');
let headerCell = null;
for (let row of table.rows) {
const firstCell = row.cells[0];
if (headerCell === null || firstCell.innerText !== headerCell.innerText) {
headerCell = firstCell;
} else {
headerCell.rowSpan++;
firstCell.remove();
}
}
table, tr, td {
border: solid 1px black;
}
<table>
<tr>
<td>fish</td>
<td>salmon</td>
</tr>
<tr>
<td>fish</td>
<td>cod</td>
</tr>
<tr>
<td>fish</td>
<td>plaice</td>
</tr>
<tr>
<td>bird</td>
<td>robin</td>
</tr>
<tr>
<td>bird</td>
<td>crow</td>
</tr>
</table>

Adding rows to table body dynamically

I am trying to add rows to an existing table that has header and footer also.
Here is my code:
<script>
function test() {
var tbl = document.getElementById("tbl");
var lastRow = tbl.rows.length - 1;
var cols = tbl.rows[lastRow].cells.length;
var row = tbl.insertRow(-1);
for (var i = 0; i < cols; i++) {
row.insertCell();
}
}
</script>
<table id="tbl" onclick="test()">
<thead>
<tr>
<th>Month</th>
<th>Savings</th>
</tr>
</thead>
<tfoot>
<tr>
<td>Sum</td>
<td>$180</td>
</tr>
</tfoot>
<tbody>
<tr>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>February</td>
<td>$80</td>
</tr>
</tbody>
</table>
when I click on any table I want to add new row to table body, but the issue here is the new row is added to table footer. please help me how to fix this issue.

You insert the row into the tBody element. Since there can be more than one tBody, you should refer to the tBodies prop of table at index 0.
var row = tbl.tBodies[0].insertRow(-1);
function test() {
var tbl = document.getElementById("tbl");
var lastRow = tbl.rows.length - 1;
var cols = tbl.rows[lastRow].cells.length;
var row = tbl.tBodies[0].insertRow(-1);
for (var i = 0; i < cols; i++) {
row.insertCell().appendChild(document.createTextNode(i));
}
}
test();
<table id="tbl" onclick="test()">
<thead>
<tr>
<th>Month</th>
<th>Savings</th>
</tr>
</thead>
<tfoot>
<tr>
<td>Sum</td>
<td>$180</td>
</tr>
</tfoot>
<tbody>
<tr>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>February</td>
<td>$80</td>
</tr>
</tbody>
</table>

Try something like this. Just clone first row and then append it as child to your table. Hope it will help you
function appendRow() {
let tbl = document.getElementById("tbl");
let newRow = tbl.rows[0].cloneNode(true);
tbl.appendChild(newRow);

How to find the corresponding th to a given td?

Basically the same question as How can I get the corresponding table header (th) from a table cell (td)? but not jQuery specific.
From a given <td> is there an easy way to find the corresponding <th>?
<table width="100%" id="stock">
<tr>
<th>Name</th>
<th>Type</th>
<th>Quantity</th>
<th>Options</th>
</tr>
<tr>
<td>foo</td>
<td id="target">bar</td>
<td>-1</td>
<td>...</td>
</tr>
I'd like something doing this:
document.getElementById('target').correspondingTH // would return HTMLObject <th>Type</th>
An ideal answer might contain both a jQuery way to do it and a vanilla one but I'm personally looking for a vanilla one.

Pure JavaScript's answer.
var index = Array.prototype.indexOf.call(your_td.parentNode.children, your_td)
var corresponding_th = document.querySelector('#your_table_id th:nth-child(' + (index+1) + ')')
As posted here in the more jQuery specifc question: https://stackoverflow.com/a/37312707/1524913

HTML table model gives easier solution. jquery in this case is more sophisticated. I tested following table:
<table style="width:100%" id="stock">
<tbody>
<tr>
<td>foo</td>
<td id="target">bar</td>
<td>-1</td>
<td>...</td>
</tr>
<tr>
<td>foo</td>
<td id="target">bar</td>
<td>-1</td>
<td>...</td>
</tr>
</tbody>
<tr>
<td>foo</td>
<td id="target">bar</td>
<td colspan="2">-1</td>
<!--<td>...</td>-->
</tr>
<thead>
<tr>
<th>Name</th>
<th>Type</th>
<th>Quantity</th>
<th>Options</th>
</tr>
</thead>
</table>
Script without jquery is simple and straightforward.
window.onload = function () {
var tbl = document.getElementById('stock');
var tds = document.getElementsByTagName('td');
for (var i = 0, td; td = tds[i]; ++i) {
td.onclick = function () {
var tr = this.parentNode;
console.log(tbl.rows[0].cells[this.cellIndex].innerHTML);
}
}
}
jquery also is useful.
$(document).ready(function () {
$('#stock td').click(function () {
console.log($(this).parents('table').find('tr:first-child').children('th:nth-child(' + (this.cellIndex + 1) + ')').html());
});
});
<thead> can be placed at the top, at the bottom, and between rows. thead inside tbody is obvious error but browser fixes it. Scripts work in any case.

I think you need to step through the TH colSpans to exactly match the TD
Try
function getHeadCell(td) {
var index = Array.prototype.indexOf.call(td.parentNode.children, td);
var table = td;
while (table && table.tagName != 'TABLE') table = table.parentNode;
var cx = 0;
for (var c = 0; cx <= index; c++) cx += table.rows[0].cells[c].colSpan;
return table.rows[0].cells[c - 1];
}
See https://jsfiddle.net/Abeeee/upt75s2x/34/ for a working example

How to copy the contents of one row in a table to another table and add the identical ones

var Sell_Button = document.getElementById('sellbtn'),
secondTable = document.getElementById("secondTableBody");
Sell_Button.addEventListener('click', function() {
var Row = secondTable.insertRow();
for (var c = 0; c < 2; c += 1) {
Row.insertCell(c);
}
Row.cells[0].innerHTML = this.parentNode.parentNode.cells[0].innerHTML;
Row.cells[2].innerHTML = this.parentNode.parentNode.cells[1].innerHTML;
//checks to see if the secondTable has a row containing the same name
for (var f = 0; f < secondTable.rows.length; f += 1) {
//adds only the sold amount if the second table has a row with the same name
//error
if (secondTable.rows[f].cells[0].innerText === this.parentNode.parentNode.cells[0].innerText) {
secondTable.rows[f].cells[1].innerHTML = +this.parentNode.parentNode.cells[2].innerHTML;
//deletes an extra row that is added at the bottom
if (secondTable.rows.length > 1) {
secondTable.deleteRow(secondTable.rows.length - 1);
}
//if nothing matched then a new row is added
} else {
secondTable.insertRow();
Row.cells[0].innerHTML = this.parentNode.parentNode.cells[0].innerHTML;
Row.cells[1].innerHTML = this.parentNode.parentNode.cells[2].innerHTML;
}
}
}
}
<html>
<body>
<div id="firstTableDiv">
<table border="1" id="firstTable">
<thead>
<th>Item</th>
<th>Stock</th>
<th colspan="1">Sold</th>
</thead>
<tbody id="firstTableBody">
<tr>
<td>Apples</td>
<td>300</td>
<td>200</td>
<td>
<button id="sellbtn">Sell</button>
</td>
</tr>
<tr>
<td>Apples</td>
<td>300</td>
<td>100</td>
<td>
<button id="sellbtn">Sell</button>
</td>
</tr>
<tr>
<td>Oranges</td>
<td>400</td>
<td>300</td>
<td>
<button id="sellbtn">Sell</button>
</td>
</tr>
</tbody>
</table>
</div>
</br>
<div id="secondTableDiv">
Sold
<table border="1" id="secondTable">
<thead>
<th>Item</th>
<th>Sold</th>
</thead>
<tbody id="secondTableBody">
</tbody>
</table>
</div>
</body>
</html>
Ok, this example isn't exactly what i'm working on but it's very similar. The only difference is that in mine the rows and buttons are dynamically added by the user and he inserts the details. What I want is that when i press on the button of each row (sell) the details (Item and Sold only) are copied into a row in the second table and checks if the same item exists in this second table if so then it adds the amount of sold of both items in one row. For instance I press on the first row button the Apples it copies the listed above details to the second table in a row and then when i click on the button of the second row (Apples also) it only adds the sold amount up and doesn't add a second apples row because an apples row already exists in the second table but when i click on the oranges button it makes a new row because the oranges row doesn't exist. So how do I do this in JavaScript? i hope i was thorough and made any sense. I have no idea why the code isn't working here but i hope you get the point. This code works perfectly just as i want it to until for some reason i get this error: Cannot read property 'innerText' of undefined when i press the buttons approx. 6-7 times targeting the if statement where i commented error.

This sets a click handler to all buttons. If the row doesn't exist in the second table it's created. It sets a data-type referring to the item. When somebody clicks the sell button again and there is a row containing the data-type the row is updated instead of created. All in plain JavaScript.
var Sell_Button = document.querySelectorAll('.sellbtn'),
secondTable = document.getElementById("secondTableBody");
Array.prototype.slice.call(Sell_Button).forEach(function(element){
element.addEventListener('click', function(e) {
//since the button is an element without children use e.
var clickedElement = e.target;
var parentRow = clickedElement.parentNode.parentNode;
//check if second table has a row with data-type
var rowWithData = secondTable.querySelector("[data-type='"+parentRow.cells[0].childNodes[0].nodeValue+"']");
if (rowWithData)
{
rowWithData.cells[1].innerHTML = parseInt(rowWithData.cells[1].childNodes[0].nodeValue) + parseInt(parentRow.cells[2].childNodes[0].nodeValue);
}
else
{
var Row = secondTable.insertRow();
Row.setAttribute("data-type", parentRow.cells[0].childNodes[0].nodeValue);
for (var c = 0; c < 2; c += 1) {
Row.insertCell(c);
}
Row.cells[0].innerHTML = parentRow.cells[0].childNodes[0].nodeValue;
Row.cells[1].innerHTML = parentRow.cells[2].childNodes[0].nodeValue;
}
});
});
<html>
<body>
<div id="firstTableDiv">
<table border="1" id="firstTable">
<thead>
<th>Item</th>
<th>Stock</th>
<th colspan="1">Sold</th>
</thead>
<tbody id="firstTableBody">
<tr>
<td>Apples</td>
<td>300</td>
<td>200</td>
<td>
<button class="sellbtn">Sell</button>
</td>
</tr>
<tr>
<td>Apples</td>
<td>300</td>
<td>100</td>
<td>
<button class="sellbtn">Sell</button>
</td>
</tr>
<tr>
<td>Oranges</td>
<td>400</td>
<td>300</td>
<td>
<button class="sellbtn">Sell</button>
</td>
</tr>
</tbody>
</table>
</div>
</br>
<div id="secondTableDiv">
Sold
<table border="1" id="secondTable">
<thead>
<th>Item</th>
<th>Sold</th>
</thead>
<tbody id="secondTableBody">
</tbody>
</table>
</div>
</body>
</html>

Do you mean something like:
$(document).on("click", "#firstTable tr button", function(b) {
b = $(this).closest("tr");
var d = $.trim(b.find("td:first").text());
b = parseFloat($.trim(b.find("td:nth-child(3)").text()));
var a = $("#secondTable"),
c = a.find("tr").filter(function(a) {
return $.trim($(this).find("td:first").text()) == d
});
c.length ? (a = c.find("td:nth-child(2)"), c = parseFloat($.trim(a.text())), a.text(b + c)) : (a = $("<tr />").appendTo(a), $("<td />", {
text: d
}).appendTo(a), $("<td />", {
text: b
}).appendTo(a))
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<div id="firstTableDiv">
<table border="1" id="firstTable">
<thead>
<tr>
<th>Item</th>
<th>Stock</th>
<th colspan="1">Sold</th>
</tr>
</thead>
<tbody id="firstTableBody">
<tr>
<td>Apples</td>
<td>300</td>
<td>200</td>
<td><button>Sell</button></td>
</tr>
<tr>
<td>Apples</td>
<td>300</td>
<td>100</td>
<td><button>Sell</button></td>
</tr>
<tr>
<td>Oranges</td>
<td>400</td>
<td>300</td>
<td><button>Sell</button></td>
</tr>
</tbody>
</table>
</div>
<br />
<div id="secondTableDiv">
Sold
<table border="1" id="secondTable">
<thead>
<tr>
<th>Item</th>
<th>Sold</th>
</tr>
</thead>
<tbody id="secondTableBody"></tbody>
</table>
</div>

Sorting pairs of rows with tablesorter

http://jsfiddle.net/9sKwJ/66/
tr.spacer { height: 40px; }
$.tablesorter.addWidget({
id: 'spacer',
format: function(table) {
var c = table.config,
$t = $(table),
$r = $t.find('tbody').find('tr'),
i, l, last, col, rows, spacers = [];
if (c.sortList && c.sortList[0]) {
$t.find('tr.spacer').removeClass('spacer');
col = c.sortList[0][0]; // first sorted column
rows = table.config.cache.normalized;
last = rows[0][col]; // text from first row
l = rows.length;
for (i=0; i < l; i++) {
// if text from row doesn't match last row,
// save it to add a spacer
if (rows[i][col] !== last) {
spacers.push(i-1);
last = rows[i][col];
}
}
// add spacer class to the appropriate rows
for (i=0; i<spacers.length; i++){
$r.eq(spacers[i]).addClass('spacer');
}
}
}
});
$('table').tablesorter({
widgets : ['spacer']
});
<table id="test">
<thead>
<tr>
<th>Name</th>
<th>Number</th>
<th>Another Example</th>
</tr>
</thead>
<tbody>
<tr>
<td>Test4</td>
<td>4</td>
<td>Hello4</td>
</tr>
<tr>
<td colspan="3">Test4</td>
</tr>
<tr>
<td>Test3</td>
<td>3</td>
<td>Hello3</td>
</tr>
<tr>
<td colspan="3">Test3</td>
</tr>
<tr>
<td>Test2</td>
<td>2</td>
<td>Hello2</td>
</tr>
<tr>
<td colspan="3">Test2</td>
</tr>
<tr>
<td>Test1</td>
<td>1</td>
<td>Hello1</td>
</tr>
<tr>
<td colspan="3">Test1</td>
</tr>
</tbody>
</table>
This sorts just the way I want it if you sort it by the first column, but the other two columns don't maintain the same paired 'tr' sort im looking for.
Any help on this?

Use the expand-child class name on each duplicated row:
<tr>
<td>Test3</td>
<td>3</td>
<td>Hello3</td>
</tr>
<tr class="expand-child">
<td colspan="3">Test3</td>
</tr>
It's defined by the cssChildRow option:
$('table').tablesorter({
cssChildRow: "expand-child"
});​
Here is a demo of it in action.