Prepend an element to a list:

Prepend a row to a matrix:

Prepend to an Association:

Define a prepend operator:

Prepend the list to a flat list, resulting in a nested list:

Prepend to a list of lists, producing a matrix:

Format the matrix:

Create a 3×3 sparse array:

Prepend a row to it, producing another sparse array:

The sparse array will revert to a normal array if the array structure cannot be maintained:

Prepend to an expression with a general head:

Prepend several rules to an Association; they are added sequentially and thus appear in reverse order:

Compare with the behavior of prepending to a list of rules:

Prepend a row to a matrix:

Prepend to each row in a matrix:

Prepend a vector to a matrix:

Successively prepend to a list:

Prepend[list,x] is equivalent to Join[{x},list]:

This is true even when x is a list:

For a general expression e, Prepend[e,x] is equivalent to Join[Head[e][x],e]:

Prepend[x][e] is equivalent to Prepend[e,x]:

When prepending to an association, if a key already exists, its value will be overwritten by the prepended value:

There is no special behavior when the first and second arguments have the same head:

It is possible to use Flatten after Prepend to effectively prepend several elements individually:

Alternatively, use Join with the arguments reversed:

When working on a shared list in parallel, Prepend is not atomic (or thread safe):

Use PrependTo in such circumstances: