numarray Manual

11.1 Introduction

numarray, like Numeric, has support for arrays of character data (provided by the numarray.strings module) in addition to arrays of numbers. The support for character arrays in Numeric is relatively limited, restricted to arrays of single characters. In contrast, numarray supports arrays of fixed length strings. As an additional enhancement, the numarray design supports interleaving arrays of characters with arrays of numbers, with both occupying the same memory buffer. This provides basic infrastructure for building the arrays of heterogenous records as provided by numarray.records (see chapter 12). Currently, neither Numeric nor numarray provides support for unicode.

Each character array is a CharArray object in the numarray.strings module. The easiest way to construct a character array is to use the numarray.strings.array() function. For example:

  >>> import numarray.strings as str
  >>> s = str.array(['Smith', 'Johnson', 'Williams', 'Miller'])
  >>> print s
  ['Smith', 'Johnson', 'Williams', 'Miller']
  >>> s.itemsize()
  8

In this example, this string array has 4 elements. The maximum string length is automatically determined from the data. In this case, the created array will support fixed length strings of 8 characters (since the longest name is 8 characters long).

The character array is just like an array in numarray, except that now each element is conceptually a Python string rather than a number. We can do the usual indexing and slicing:

  >>> print s[0]
  'Smith'
  >>> print s[:2]
  ['Smith', 'Johnson']
  >>> s[:2] = 'changed'
  >>> print s
  ['changed', 'changed', 'Williams', 'Miller']

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