MapAt[f, expr, n] applies f to the element at position n in expr. If n is negative, the position is counted from the end. MapAt[f, expr, {i, j, ...}] applies f to the part of ...

Select the next-higher subexpression by pressing Ctrl+.. Press Ctrl+. repeatedly. Get rid of the contents of an expression and destructure it by pressing Del (or Backspace).

Prepend[expr, elem] gives expr with elem prepended.

ButtonBox[boxes] is a low-level box construct that represents a button in a notebook expression.

CellAutoOverwrite is an option for Cell which specifies whether an output cell should be overwritten by new output when the preceding input cell is evaluated.

Mathematica provides several convenient methods for extracting and manipulating parts of matrices. The flexible [[ ]] (Part) and ;; (Span) syntaxes provide compact yet ...

DeleteBorderComponents[image] replaces connected components adjacent to the border in a binary image image with background pixels.DeleteBorderComponents[m] replaces ...

Finding elements that match a pattern. This gives the elements of the list which match the pattern x^_. Here is the total number of elements which match the pattern.

The raw SQL command DELETE deletes data from a database. An alternative is to use the Mathematica command SQLDelete, described in "Deleting Data". If you find that the ...

Diagonal[m] gives the list of elements on the leading diagonal of the matrix m.Diagonal[m, k] gives the elements on the k\[Null]^th diagonal of m.