Numpy recarray.tostring() function | Python

In numpy, arrays may have a data-types containing fields, analogous to columns in a spreadsheet. An example is [(a, int), (b, float)], where each entry in the array is a pair of (int, float). Normally, these attributes are accessed using dictionary lookups such as arr[‘a’] and arr[‘b’]. Record arrays allow the fields to be accessed as members of the array, using arr.a and arr.b. numpy.recarray.tostring() function construct Python bytes containing the raw data bytes in the array.

Syntax : numpy.recarray.tostring(order=’C’) Parameters: order : [‘C’, ‘F’, None, optional] Order of the data for multidimensional arrays: C, Fortran, or the same as for the original array. Return : [bytes] Python bytes exhibiting a copy of record array’s raw data.

Code #1 : 

Python3

# Python program explaining
# numpy.recarray.tostring() method

# importing numpy as geek
import numpy as geek

# creating input array with 2 different field
in_arr = geek.array([[(5.0, 2), (3.0, -4), (6.0, 9)],
                     [(9.0, 1), (5.0, 4), (-12.0, -7)]],
                     dtype =[('a', float), ('b', int)])

print ("Input array : ", in_arr)

# convert it to a record array,
# using arr.view(np.recarray)
rec_arr = in_arr.view(geek.recarray)
print("Record array of float: ", rec_arr.a)
print("Record array of int: ", rec_arr.b)

# applying recarray.tostring methods
# to float record array in default order
out_arr = rec_arr.a.tostring()
print ("Output Python bytes of float record array in default order ", out_arr)
print()

# applying recarray.tostring methods
# to float record array in fortran order
out_arr = rec_arr.a.tostring(order ='F')
print ("Output Python bytes of float record array in fortran order ", out_arr)
print()

# applying recarray.tostring methods
# to int record array in default order
out_arr = rec_arr.b.tostring()
print ("Output Python bytes of int record array in default order ", out_arr)
print()

# applying recarray.tostring methods
# to int record array in fortran order
out_arr = rec_arr.b.tostring(order ='F')
print ("Output Python bytes of int record array in fortran order ", out_arr)

Output:

Input array : [[( 5., 2) ( 3., -4) ( 6., 9)] [( 9., 1) ( 5., 4) (-12., -7)]] Record array of float: [[ 5. 3. 6.] [ 9. 5. -12.]] Record array of int: [[ 2 -4 9] [ 1 4 -7]] Output Python bytes of float record array in default order b’\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x00\x08@\x00\x00\x00\x00\x00\x00\x18@\x00\x00\x00\x00\x00\x00″@\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x00(\xc0′ Output Python bytes of float record array in fortran order b’\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x00″@\x00\x00\x00\x00\x00\x00\x08@\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x00\x18@\x00\x00\x00\x00\x00\x00(\xc0′ Output Python bytes of int record array in default order b’\x02\x00\x00\x00\xfc\xff\xff\xff\t\x00\x00\x00\x01\x00\x00\x00\x04\x00\x00\x00\xf9\xff\xff\xff’ Output Python bytes of int record array in fortran order b’\x02\x00\x00\x00\x01\x00\x00\x00\xfc\xff\xff\xff\x04\x00\x00\x00\t\x00\x00\x00\xf9\xff\xff\xff’

Code #2 : We are applying numpy.recarray.tostring() to whole record array. 

Python3

# Python program explaining
# numpy.recarray.tostring() method

# importing numpy as geek
import numpy as geek

# creating input array with 2 different field
in_arr = geek.array([[(5.0, 2), (3.0, 4), (6.0, -7)],
                     [(9.0, 1), (6.0, 4), (-2.0, -7)]],
                     dtype =[('a', float), ('b', int)])

print ("Input array : ", in_arr)

# convert it to a record array,
# using arr.view(np.recarray)
rec_arr = in_arr.view(geek.recarray)

# applying recarray.tostring methods to
# record array in default order
out_arr = rec_arr.tostring()
print ("Output Python bytes of record array in default order ", out_arr)
print()

# applying recarray.tostring methods to
# record array in fortran order
out_arr = rec_arr.tostring(order ='F')
print ("Output Python bytes of record array in fortran order ", out_arr)

Output:

Input array : [[( 5., 2) ( 3., 4) ( 6., -7)] [( 9., 1) ( 6., 4) (-2., -7)]] Output Python bytes of record array in default order b’\x00\x00\x00\x00\x00\x00\x14@\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08@\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x18@\xf9\xff\xff\xff\x00\x00\x00\x00\x00\x00″@\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x18@\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xc0\xf9\xff\xff\xff’ Output Python bytes of record array in fortran order b’\x00\x00\x00\x00\x00\x00\x14@\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00″@\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08@\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x18@\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x18@\xf9\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\xc0\xf9\xff\xff\xff’