emacs: transposing text

Transposing text is the act of swapping two syntactic units of text with one another.

Key Binding	Purpose
C-t	Transpose characters
M-t	Transpose words
C-M-t	Transpose s-expression
C-x C-t	Transpose lines
M-x transpose-paragraphs	Transpose paragraphs
M-x transpose-sentences	Transpose sentences

C-t: Transpose Characters

A█BC

After C-t:

BA█C

Note that the point moved forward one character so you can repeat calls to C-t to “pull” the character to the right:

BCA█

When you are at the end of a line. C-t will swap the two characters to the left of the point:

BCA█

After C-t:

BAC█

This asymmetry is a surprisingly useful way of fixing typos as they occur. Fixing mistyped characters with C-t is a useful time saver as it saves you the effort of deleting both characters and retyping them.

M-t: Transpose Words

Transposing two words with M-t works as you would expect when the words are plain text, like this:

Hello █World

After M-t:

World Hello█

Consider this example Python code where we have a dictionary (a key-value hash map):

names = {
'Jerry':█ 'Seinfeld', 
'Cosmo': 'Kramer',
}

With the point between the key and value, a call to M-t is pure magic:

names = {
'Seinfeld': 'Jerry', 
'Cosmo': 'Kramer',
}

C-M-t: Transpose S-expressions

Consider what happens if we mix a balanced expression with a word:

Hello,█ (insert name here)!

After C-M-t:

(insert name here), Hello█!

Other Transpose Commands

Transposing lines with C-x C-t is useful however. I use it frequently to re-order newline-based lists and it’s also useful for swapping around variable assignments; changing the order functions are called, and so on.