the_martian - 1 year ago 361
Python Question

# Python to Matlab Conversion?

I have this python code here below (for bubble sort). Below that is my attempt at converting it to MATLAB code. I'm new to MATLAB, and I'm doing the conversion for practice. I would appreciate feedback on how accurate/incorrect my conversion is.

The python version:

``````def bubble_sort(alist):
return bubble_sort_helper(alist, len(alist))
def bubble_sort_helper(alist, n):
if n < 2:
return alist
for i in range(len(alist)-1):
if alist[i] > alist[i+1]:
temp = alist[i]
alist[i] = alist[i+1]
alist[i+1] = temp
return bubble_sort_helper(alist, n-1)
``````

My attempt at a MATLAB conversion:

``````function a = bubble_sort(alist)
a = bubble_sort_helper(alist, size(alist))
end

function b = bubble_sort_helper(alist, n)
if n < 2
b = alist
end
for ii = size(alist)
if alist(1) > alist (ii+1)
temp = alist(ii)
alist(ii) = alist(ii+1)
alist(ii+1) = temp
end
end
b = bubble_sort_helper(alistn n-1)

end
``````

A few issues here:

1. You need to use `numel` rather than `size` to get the number of elements in an array. `size` will give you a vector of sizes of each dimension and `numel` will give you the total number of elements

2. You need to actually create an array of values for your `for` loop to loop through. To do this, use the colon to create an array from `2` to `n`.

``````for ii = 2:n
end
``````
3. You use `ii` as your looping variable but try to use `i` inside of the loop. Pick one and stick to it (preferably not `i`)

4. To flip the values you can simply do your assignment like this:

``````alist([i-1, i]) = alist([i, i-1]);
``````

Taken together, this will give you something like this:

``````function a = bubble_sort(alist)
a = bubble_sort_helper(alist, numel(alist))
end

function b = bubble_sort_helper(alist, n)
if n < 2
b = alist;
else
for k = 2:n
if alist(k-1) > alist(k)
alist([k-1, k]) = alist([k, k-1]);
end
end
b = bubble_sort_helper(alist, n-1);
end
end
``````
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