gives the number of elements in expr.



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Basic Examples  (2)

Find the length of a list:

Find the length of an Association:

Scope  (2)

Length works with any head:

Length[expr] gives the number of elements in the top level of expr:

Generalizations & Extensions  (5)

The length of a symbol is 0:

The length of a string is 0:

StringLength gives the number of characters:

Explicit numbers have length 0:

Length works on SparseArray objects:

Length works on structured arrays, like SymmetrizedArray objects:

Applications  (5)

Find the number of rows in a matrix:

Find the length of each sublist:

Find the number of terms in a polynomial:

Find the number of digits in 1000!:

Get the number of points used to plot a curve:

Properties & Relations  (2)

Length gives the maximum index that can be used:

For expressions with length greater than 0, Length[expr] equals First[Dimensions[expr]]:

Possible Issues  (5)

Length operates on the FullForm of expressions, not their displayed form:

Rational and complex numbers are atoms, so they have length 0:

Numeric expressions are treated like other expressions, not like explicit numbers:

Length counts only "arguments", not parts of heads:

For nonatomic e, Length[e] is equivalent to First[Dimensions[e]]:

Introduced in 1988
Updated in 2003