BUILT-IN MATHEMATICA SYMBOL

PrependTo

prepends elem to the value of s, and resets s to the result.

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

PrependTo works on SparseArray objects, returning ordinary lists if necessary. »

Assign l to a list:

Include a new value at the beginning of the list:

The value assigned to l has changed:

Assign l to a list:

Out[1]=

Include a new value at the beginning of the list:

Out[2]=

The value assigned to l has changed:

Out[3]=

Use a head other than List:

This assigns s to a sparse matrix:

Add a row to the top of the matrix:

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

Assign m to be a 2×2 matrix:

Prepend a row to m:

Prepend 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 prepended to:

Something for which

AtomQ is True cannot be prepended to:

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

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