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Capitalize

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

Capitalize["string"]

Gives "string" with its first character in uppercase.

Capitalize[{s1, s2, ...}]

Capitalizes each string.

Examples (10)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (3)

In[1]:= Capitalize["hello world"]
Out[1]= "Hello world"

In[2]:= Capitalize["élan"]
Out[2]= "Élan"

In[3]:= Decapitalize[{"Alpha", "Beta"}]
Out[3]= {"alpha", "beta"}

Applications (7)

Only the first character changes

In[4]:= Capitalize["hello world"]
Out[4]= "Hello world"

In[5]:= Capitalize["élan vital"]
Out[5]= "Élan vital"

The first character uses the full mapping, so it can expand

In[6]:= Capitalize["ßx"]
Out[6]= "SSx"

A list of strings maps

In[7]:= Capitalize[{"alpha", "beta", "gamma"}]
Out[7]= {"Alpha", "Beta", "Gamma"}

In[8]:= Capitalize[""]
Out[8]= ""

Title case, word by word

In[9]:= StringRiffle[Capitalize /@ StringSplit["the quick brown fox"]]
Out[9]= "The Quick Brown Fox"

Not a string: Capitalize::strse, unevaluated

In[10]:= Capitalize[5]
Out[10]= Capitalize[5]

Implementation notes

Algorithm. builtin_capitalize calls capitalize_builtin(res, "Capitalize", 1). A String argument goes to the shared case kernel map_case(s, len, 1, 0, 1) — the same routine as ToUpperCase, restricted by its from/count window to character 0, so only the first code point is looked up in k_upper_map and every later byte is copied verbatim. A flat List of strings (checked by is_string_list) is mapped element by element into a new List; anything else emits Capitalize::strse through strings_arg_message (the mth_message funnel) and stays unevaluated.

Data structures. The generated full-case-mapping table k_upper_map (U8CaseMap records, Unicode 16.0.0, from tools/gen_unicode_tables.py), searched by binary search; ASCII is mapped inline. The first character may expand to up to three code points (Capitalize["ßx"] is "SSx").

Complexity / limits. One O(L) copy of the string plus one O(log M) table lookup. It applies the uppercase mapping, not Unicode titlecasing. Not Listable: nested or mixed lists are rejected rather than threaded. No numeric (packed / Compile[]) surface.

Attributes: Protected.

References

See also: Decapitalize

Notes & additional examples

Notes

  • Maps only the first character, with the same full Unicode uppercase table as ToUpperCase; the rest of the string is copied byte for byte.
  • It uses the uppercase, not the Unicode titlecase, mapping.
  • Accepts a string or a flat list of strings; it is not Listable, so a mixed or nested list emits Capitalize::strse and stays unevaluated.
  • Attributes {Protected}.
  • See also: Decapitalize, ToUpperCase.