Built-in Mathematica Symbol

AppendTo

AppendTo[s, elem]
appends elem to the value of s, and resets s to the result.

You can use AppendTo repeatedly to build up a list, though Sow and Reap will usually be more efficient. »

Assign l to a list:

Include a new value at the end of the list:

The value assigned to l has changed:

Assign l to a list:

Include a new value at the end of the list:

The value assigned to l has changed:

Use a head other than List:

This assigns s to a sparse matrix:

Add a row to the matrix:

Appending an element with inconsistent dimensions requires converting to ordinary lists:

Assign m to be a 2×2 matrix:

Append a row to m:

Append a column to m:

m is now a 3×3 matrix:

The first argument must be a variable:

The first argument must be a variable with a value:

The first argument must be assigned to something which can be appended to:

Something for which AtomQ is True cannot be appended to:

Using AppendTo to accumulate values in large loops can be slow:

There are many alternatives, such as using Reap and Sow: