numpy.chararray#

class numpy.chararray(shape, itemsize=1, unicode=False, buffer=None, offset=0, strides=None, order=None)[source]#

Provides a convenient view on arrays of string and unicode values.

Note

The chararray class exists for backwards compatibility with Numarray, it is not recommended for new development. Starting from numpy 1.4, if one needs arrays of strings, it is recommended to use arrays of dtype object_, string_ or unicode_, and use the free functions in the numpy.char module for fast vectorized string operations.

Versus a regular NumPy array of type str or unicode, this class adds the following functionality:

  1. values automatically have whitespace removed from the end when indexed

  2. comparison operators automatically remove whitespace from the end when comparing values

  3. vectorized string operations are provided as methods (e.g. endswith) and infix operators (e.g. "+", "*", "%")

chararrays should be created using numpy.char.array or numpy.char.asarray, rather than this constructor directly.

This constructor creates the array, using buffer (with offset and strides) if it is not None. If buffer is None, then constructs a new array with strides in “C order”, unless both len(shape) >= 2 and order='F', in which case strides is in “Fortran order”.

Parameters:
shapetuple

Shape of the array.

itemsizeint, optional

Length of each array element, in number of characters. Default is 1.

unicodebool, optional

Are the array elements of type unicode (True) or string (False). Default is False.

bufferobject exposing the buffer interface or str, optional

Memory address of the start of the array data. Default is None, in which case a new array is created.

offsetint, optional

Fixed stride displacement from the beginning of an axis? Default is 0. Needs to be >=0.

stridesarray_like of ints, optional

Strides for the array (see ndarray.strides for full description). Default is None.

order{‘C’, ‘F’}, optional

The order in which the array data is stored in memory: ‘C’ -> “row major” order (the default), ‘F’ -> “column major” (Fortran) order.

Examples

>>> charar = np.chararray((3, 3))
>>> charar[:] = 'a'
>>> charar
chararray([[b'a', b'a', b'a'],
           [b'a', b'a', b'a'],
           [b'a', b'a', b'a']], dtype='|S1')

>>> charar = np.chararray(charar.shape, itemsize=5)
>>> charar[:] = 'abc'
>>> charar
chararray([[b'abc', b'abc', b'abc'],
           [b'abc', b'abc', b'abc'],
           [b'abc', b'abc', b'abc']], dtype='|S5')
Attributes:
T

View of the transposed array.

base

Base object if memory is from some other object.

ctypes

An object to simplify the interaction of the array with the ctypes module.

data

Python buffer object pointing to the start of the array’s data.

dtype

Data-type of the array’s elements.

flags

Information about the memory layout of the array.

flat

A 1-D iterator over the array.

imag

The imaginary part of the array.

itemsize

Length of one array element in bytes.

nbytes

Total bytes consumed by the elements of the array.

ndim

Number of array dimensions.

real

The real part of the array.

shape

Tuple of array dimensions.

size

Number of elements in the array.

strides

Tuple of bytes to step in each dimension when traversing an array.

Methods

astype(dtype[, order, casting, subok, copy])

Copy of the array, cast to a specified type.

argsort([axis, kind, order])

Returns the indices that would sort this array.

copy([order])

Return a copy of the array.

count(sub[, start, end])

Returns an array with the number of non-overlapping occurrences of substring sub in the range [start, end].

decode([encoding, errors])

Calls bytes.decode element-wise.

dump(file)

Dump a pickle of the array to the specified file.

dumps()

Returns the pickle of the array as a string.

encode([encoding, errors])

Calls str.encode element-wise.

endswith(suffix[, start, end])

Returns a boolean array which is True where the string element in self ends with suffix, otherwise False.

expandtabs([tabsize])

Return a copy of each string element where all tab characters are replaced by one or more spaces.

fill(value)

Fill the array with a scalar value.

find(sub[, start, end])

For each element, return the lowest index in the string where substring sub is found.

flatten([order])

Return a copy of the array collapsed into one dimension.

getfield(dtype[, offset])

Returns a field of the given array as a certain type.

index(sub[, start, end])

Like find, but raises ValueError when the substring is not found.

isalnum()

Returns true for each element if all characters in the string are alphanumeric and there is at least one character, false otherwise.

isalpha()

Returns true for each element if all characters in the string are alphabetic and there is at least one character, false otherwise.

isdecimal()

For each element in self, return True if there are only decimal characters in the element.

isdigit()

Returns true for each element if all characters in the string are digits and there is at least one character, false otherwise.

islower()

Returns true for each element if all cased characters in the string are lowercase and there is at least one cased character, false otherwise.

isnumeric()

For each element in self, return True if there are only numeric characters in the element.

isspace()

Returns true for each element if there are only whitespace characters in the string and there is at least one character, false otherwise.

istitle()

Returns true for each element if the element is a titlecased string and there is at least one character, false otherwise.

isupper()

Returns true for each element if all cased characters in the string are uppercase and there is at least one character, false otherwise.

item(*args)

Copy an element of an array to a standard Python scalar and return it.

join(seq)

Return a string which is the concatenation of the strings in the sequence seq.

ljust(width[, fillchar])

Return an array with the elements of self left-justified in a string of length width.

lower()

Return an array with the elements of self converted to lowercase.

lstrip([chars])

For each element in self, return a copy with the leading characters removed.

nonzero()

Return the indices of the elements that are non-zero.

put(indices, values[, mode])

Set a.flat[n] = values[n] for all n in indices.

ravel([order])

Return a flattened array.

repeat(repeats[, axis])

Repeat elements of an array.

replace(old, new[, count])

For each element in self, return a copy of the string with all occurrences of substring old replaced by new.

reshape(shape[, order])

Returns an array containing the same data with a new shape.

resize(new_shape[, refcheck])

Change shape and size of array in-place.

rfind(sub[, start, end])

For each element in self, return the highest index in the string where substring sub is found, such that sub is contained within [start, end].

rindex(sub[, start, end])

Like rfind, but raises ValueError when the substring sub is not found.

rjust(width[, fillchar])

Return an array with the elements of self right-justified in a string of length width.

rsplit([sep, maxsplit])

For each element in self, return a list of the words in the string, using sep as the delimiter string.

rstrip([chars])

For each element in self, return a copy with the trailing characters removed.

searchsorted(v[, side, sorter])

Find indices where elements of v should be inserted in a to maintain order.

setfield(val, dtype[, offset])

Put a value into a specified place in a field defined by a data-type.

setflags([write, align, uic])

Set array flags WRITEABLE, ALIGNED, WRITEBACKIFCOPY, respectively.

sort([axis, kind, order])

Sort an array in-place.

split([sep, maxsplit])

For each element in self, return a list of the words in the string, using sep as the delimiter string.

splitlines([keepends])

For each element in self, return a list of the lines in the element, breaking at line boundaries.

squeeze([axis])

Remove axes of length one from a.

startswith(prefix[, start, end])

Returns a boolean array which is True where the string element in self starts with prefix, otherwise False.

strip([chars])

For each element in self, return a copy with the leading and trailing characters removed.

swapaxes(axis1, axis2)

Return a view of the array with axis1 and axis2 interchanged.

swapcase()

For each element in self, return a copy of the string with uppercase characters converted to lowercase and vice versa.

take(indices[, axis, out, mode])

Return an array formed from the elements of a at the given indices.

title()

For each element in self, return a titlecased version of the string: words start with uppercase characters, all remaining cased characters are lowercase.

tofile(fid[, sep, format])

Write array to a file as text or binary (default).

tolist()

Return the array as an a.ndim-levels deep nested list of Python scalars.

tostring([order])

A compatibility alias for tobytes, with exactly the same behavior.

translate(table[, deletechars])

For each element in self, return a copy of the string where all characters occurring in the optional argument deletechars are removed, and the remaining characters have been mapped through the given translation table.

transpose(*axes)

Returns a view of the array with axes transposed.

upper()

Return an array with the elements of self converted to uppercase.

view([dtype][, type])

New view of array with the same data.

zfill(width)

Return the numeric string left-filled with zeros in a string of length width.