Python – Can parallel traversals be done in MATLAB just as in Python

arraysfor-loopmatlabpython

Using the zip function, Python allows for loops to traverse multiple sequences in parallel.

for (x,y) in zip(List1, List2):

Does MATLAB have an equivalent syntax? If not, what is the best way to iterate over two parallel arrays at the same time using MATLAB?

Best Solution

If x and y are column vectors, you can do:

for i=[x';y']
# do stuff with i(1) and i(2)
end

(with row vectors, just use x and y).

Here is an example run:

>> x=[1 ; 2; 3;]

x =

     1
     2
     3

>> y=[10 ; 20; 30;]

y =

    10
    20
    30

>> for i=[x';y']
disp(['size of i = ' num2str(size(i)) ', i(1) = ' num2str(i(1)) ', i(2) = ' num2str(i(2))])
end
size of i = 2  1, i(1) = 1, i(2) = 10
size of i = 2  1, i(1) = 2, i(2) = 20
size of i = 2  1, i(1) = 3, i(2) = 30
>>

Related Solutions

Python – Can someone explain all in Python

Linked to, but not explicitly mentioned here, is exactly when __all__ is used. It is a list of strings defining what symbols in a module will be exported when from <module> import * is used on the module.

For example, the following code in a foo.py explicitly exports the symbols bar and baz:

__all__ = ['bar', 'baz']

waz = 5
bar = 10
def baz(): return 'baz'

These symbols can then be imported like so:

from foo import *

print(bar)
print(baz)

# The following will trigger an exception, as "waz" is not exported by the module
print(waz)

If the __all__ above is commented out, this code will then execute to completion, as the default behaviour of import * is to import all symbols that do not begin with an underscore, from the given namespace.

Reference: https://docs.python.org/tutorial/modules.html#importing-from-a-package

NOTE: __all__ affects the from <module> import * behavior only. Members that are not mentioned in __all__ are still accessible from outside the module and can be imported with from <module> import <member>.

Python – difference between “==” and “is”

is will return True if two variables point to the same object, == if the objects referred to by the variables are equal.

>>> a = [1, 2, 3]
>>> b = a
>>> b is a 
True
>>> b == a
True

# Make a new copy of list `a` via the slice operator, 
# and assign it to variable `b`
>>> b = a[:] 
>>> b is a
False
>>> b == a
True

In your case, the second test only works because Python caches small integer objects, which is an implementation detail. For larger integers, this does not work:

>>> 1000 is 10**3
False
>>> 1000 == 10**3
True

The same holds true for string literals:

>>> "a" is "a"
True
>>> "aa" is "a" * 2
True
>>> x = "a"
>>> "aa" is x * 2
False
>>> "aa" is intern(x*2)
True

Please see this question as well.

Best Solution

Related Solutions

Python – Can someone explain __all__ in Python

Python – difference between “==” and “is”

Related Question

Python – Can someone explain all in Python