length
The length function.
Syntax

length(X)

X
is a string, vector, matrix, list, set, or pixmap

Description
In general, if X
is a container, then length(X)
is the number of elements it contains. Depending on the type of X
, this number is typically referred to as the “cardinality”, “dimension”, “length”, or “size” of X
.

If
s
is a string, thenlength(s)
is the length ofs
, that is, the number of characters ins
. 
If
v
is a vector, thenlength(v)
is the dimension ofv
, that is, the number of entries, or components, ofv
. 
If
A
is a matrix, thenlength(A)
is the number of entries inA
. 
If
L
is a list, thenlength(L)
is the number of elements ofL
. 
If
S
is a set, thenlength(S)
is the cardinality ofS
, that is, the number of elements ofS
. 
If
pm
is a pixmap, thenlength(pm)
is the number of pixels inpm
.
Notes
The prefix operator #
is mapped to the length
function.
card and cardinality are synonyms of length.
Examples
P ≔ filter(SequenceList(1000), IsPrime); #P
168
#functions()
781
f ≔ n ↦ if(even(n), n/2, 3⋅n + 1);
#orbit(f, 1000)
112
A ≔ ❨❨6, 3, 2, 0, 4, 5❩, ❨7, 0, 2, 1, 4, 2❩, ❨6, 2, 3, 1, 4, 2❩, ❨8, 0, 2, 3, 3, 5❩, ❨4, 2, 6, 3, 2, 0❩❩
⎛6 3 2 0 4 5⎞ ⎜7 0 2 1 4 2⎟ ⎜6 2 3 1 4 2⎟ ⎜8 0 2 3 3 5⎟ ⎝4 2 6 3 2 0⎠
#A
30