numpy.chararray

class numpy.chararray

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='Fortran', in which case strides is in “Fortran order”.

Parameters:

shape : tuple

Shape of the array.

itemsize : int, optional

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

unicode : bool, optional

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

buffer : int, optional

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

offset : int, optional

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

strides : array_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([['a', 'a', 'a'],
       ['a', 'a', 'a'],
       ['a', 'a', 'a']],
      dtype='|S1')

>>> charar = np.chararray(charar.shape, itemsize=5)
>>> charar[:] = 'abc'
>>> charar
chararray([['abc', 'abc', 'abc'],
       ['abc', 'abc', 'abc'],
       ['abc', 'abc', 'abc']],
      dtype='|S5')

Attributes

T	Same as self.transpose(), except that self is returned if self.ndim < 2.
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.
copy([order])	Return a copy of the array.
dump(file)	Dump a pickle of the array to the specified file.
dumps()	Returns the pickle of the array as a string.
fill(value)	Fill the array with a scalar value.
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.
item(*args)	Copy an element of an array to a standard Python scalar and return it.
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.
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.
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, and UPDATEIFCOPY, respectively.
sort([axis, kind, order])	Sort an array, in-place.
squeeze([axis])	Remove single-dimensional entries from the shape of a.
swapaxes(axis1, axis2)	Return a view of the array with axis1 and axis2 interchanged.
take(indices[, axis, out, mode])	Return an array formed from the elements of a at the given indices.
tofile(fid[, sep, format])	Write array to a file as text or binary (default).
tolist()	Return the array as a (possibly nested) list.
tostring([order])	Construct Python bytes containing the raw data bytes in the array.
transpose(*axes)	Returns a view of the array with axes transposed.
view([dtype, type])	New view of array with the same data.

argsort