numpy ndarray 数组对象

https://docs.scipy.org/doc/numpy/reference/arrays.ndarray.html

注意arange等函数生成的对象没有维度.既.shape属性,第二个数字是空.要用reshape来将它转换为多维度,这样才能像矩阵那样操作.

创建数组

自动生成数组

name	describe
empty(shape[, dtype, order])	生成给定形状的数组,数组数据是随机数
empty_like(a[, dtype, order, subok])	Return a new array with the same shape and type as a given array.
eye(N[, M, k, dtype])	Return a 2-D array with ones on the diagonal and zeros elsewhere.
identity(n[, dtype])	Return the identity array.
ones(shape[, dtype, order])	生成给定形状的数组,数组的数据是1
ones_like(a[, dtype, order, subok])	Return an array of ones with the same shape and type as a given array.
zeros(shape[, dtype, order])	生成给定形状的数组,数组的数据是0
zeros_like(a[, dtype, order, subok])	Return an array of zeros with the same shape and type as a given array.
full(shape, fill_value[, dtype, order])	生成给定形状的数组,数组的数据用fill_value填充
full_like(a, fill_value[, dtype, order, subok])	Return a full array with the same shape and type as a given array.
arange([start,] stop[, step,][, dtype])	生成等差数组,设定步长
linspace(start, stop[, num, endpoint, …])	生成等差数组,设定生成的数目
logspace(start, stop[, num, endpoint, base, …])	Return numbers spaced evenly on a log scale.
geomspace(start, stop[, num, endpoint, dtype])	Return numbers spaced evenly on a log scale (a geometric progression).
meshgrid(*xi, **kwargs)	Return coordinate matrices from coordinate vectors.
mgrid	nd_grid instance which returns a dense multi-dimensional “meshgrid”.)
ogrid	nd_grid instance which returns an open multi-dimensional “meshgrid”.)

从已有数据转化为数组

name	describe
array(object[, dtype, copy, order, subok, ndmin])	Create an array.
asarray(a[, dtype, order])	Convert the input to an array.
asanyarray(a[, dtype, order])	Convert the input to an ndarray, but pass ndarray subclasses through.
ascontiguousarray(a[, dtype])	Return a contiguous array in memory (C order).
asmatrix(data[, dtype])	Interpret the input as a matrix.
copy(a[, order])	Return an array copy of the given object.
frombuffer(buffer[, dtype, count, offset])	Interpret a buffer as a 1-dimensional array.
fromfile(file[, dtype, count, sep])	Construct an array from data in a text or binary file.
fromfunction(function, shape, **kwargs)	Construct an array by executing a function over each coordinate.
fromiter(iterable, dtype[, count])	Create a new 1-dimensional array from an iterable object.
fromstring(string[, dtype, count, sep])	A new 1-D array initialized from raw binary or text data in a string.
loadtxt(fname[, dtype, comments, delimiter, …])	Load data from a text file.

数组属性

属性	描述
Memory layout
ndarray.flags	Information about the memory layout of the array.
ndarray.shape	Tuple of array dimensions.
ndarray.strides	Tuple of bytes to step in each dimension when traversing an array.
ndarray.ndim	Number of array dimensions.
ndarray.data	Python buffer object pointing to the start of the array’s data.
ndarray.size	Number of elements in the array.
ndarray.itemsize	Length of one array element in bytes.
ndarray.nbytes	Total bytes consumed by the elements of the array.
ndarray.base	Base object if memory is from some other object.
Data type
ndarray.dtype	Data-type of the array’s elements.
Other attributes
ndarray.T	Same as self.transpose(), except that self is returned if self.ndim < 2.
ndarray.real	The real part of the array.
ndarray.imag	The imaginary part of the array.
ndarray.flat	A 1-D iterator over the array.
ndarray.ctypes	An object to simplify the interaction of the array with the ctypes module.
ctypes foreign function interface
ndarray.ctypes	An object to simplify the interaction of the array with the ctypes module.

数组方法

数组转换

方法	描述
ndarray.item(*args)	Copy an element of an array to a standard Python scalar and return it.
ndarray.tolist()	Return the array as a (possibly nested) list.
ndarray.itemset(*args)	Insert scalar into an array (scalar is cast to array’s dtype, if possible)
ndarray.tostring([order])	Construct Python bytes containing the raw data bytes in the array.
ndarray.tobytes([order])	Construct Python bytes containing the raw data bytes in the array.
ndarray.tofile(fid[, sep, format])	Write array to a file as text or binary (default).
ndarray.dump(file)	Dump a pickle of the array to the specified file.
ndarray.dumps()	Returns the pickle of the array as a string.
ndarray.astype(dtype[, order, casting, …])	Copy of the array, cast to a specified type.
ndarray.byteswap(inplace)	Swap the bytes of the array elements
ndarray.copy([order])	Return a copy of the array.
ndarray.view([dtype, type])	New view of array with the same data.
ndarray.getfield(dtype[, offset])	Returns a field of the given array as a certain type.
ndarray.setflags([write, align, uic])	Set array flags WRITEABLE, ALIGNED, and UPDATEIFCOPY, respectively.
ndarray.fill(value)	Fill the array with a scalar value.

形状操作

方法	描述
ndarray.reshape(shape[, order])	Returns an array containing the same data with a new shape.
ndarray.resize(new_shape[, refcheck])	Change shape and size of array in-place.
ndarray.transpose(*axes)	Returns a view of the array with axes transposed.
ndarray.swapaxes(axis1, axis2)	Return a view of the array with axis1 and axis2 interchanged.
ndarray.flatten([order])	Return a copy of the array collapsed into one dimension.
ndarray.ravel([order])	Return a flattened array.
ndarray.squeeze([axis])	Remove single-dimensional entries from the shape of a.

元素选择和操作

方法	操作
ndarray.take(indices[, axis, out, mode])	Return an array formed from the elements of a at the given indices.
ndarray.put(indices, values[, mode])	Set a.flat[n] = values[n] for all n in indices.
ndarray.repeat(repeats[, axis])	复制数组里面的值
ndarray.choose(choices[, out, mode])	Use an index array to construct a new array from a set of choices.
ndarray.sort([axis, kind, order])	Sort an array, in-place.
ndarray.argsort([axis, kind, order])	Returns the indices that would sort this array.
ndarray.partition(kth[, axis, kind, order])	Rearranges the elements in the array in such a way that value of the element in kth position is in the position it would be in a sorted array.
ndarray.argpartition(kth[, axis, kind, order])	Returns the indices that would partition this array.
ndarray.searchsorted(v[, side, sorter])	Find indices where elements of v should be inserted in a to maintain order.
ndarray.nonzero()	Return the indices of the elements that are non-zero.
ndarray.compress(condition[, axis, out])	Return selected slices of this array along given axis.
ndarray.diagonal([offset, axis1, axis2])	返回对角线元素

计算

方法	描述
ndarray.argmax([axis, out])	返回序列中第一个最大值的索引
ndarray.min([axis, out, keepdims])	返回最小值
ndarray.argmin([axis, out])	返回序列中第一个最小值的索引
ndarray.ptp([axis, out])	Peak to peak (maximum - minimum) 最大值减最小值，幅度
ndarray.clip([min, max, out])	Return an array whose values are limited to [min, max].
ndarray.conj()	Complex-conjugate all elements.
ndarray.round([decimals, out])	Return a with each element rounded to the given number of decimals.
ndarray.trace([offset, axis1, axis2, dtype, out])	Return the sum along diagonals of the array.
ndarray.sum([axis, dtype, out, keepdims])	Return the sum of the array elements over the given axis.
ndarray.cumsum([axis, dtype, out])	Return the cumulative sum of the elements along the given axis.
ndarray.mean([axis, dtype, out, keepdims])	Returns the average of the array elements along given axis.
ndarray.var([axis, dtype, out, ddof, keepdims])	Returns the variance of the array elements, along given axis.
ndarray.std([axis, dtype, out, ddof, keepdims])	Returns the standard deviation of the array elements along given axis.
ndarray.prod([axis, dtype, out, keepdims])	Return the product of the array elements over the given axis
ndarray.cumprod([axis, dtype, out])	Return the cumulative product of the elements along the given axis.
ndarray.all([axis, out, keepdims])	Returns True if all elements evaluate to True.
ndarray.any([axis, out, keepdims])	Returns True if any of the elements of a evaluate to True.