Help with a piece of code

Hey all, I'm working on a school project that's about changing the order of characters in a binary array. In the process of writing it, I found a bit of code online to help me:

v = sprintf('%d', array3)
endarray = v - '0'

Basically, what this does is it takes the value of array3, which for example is [1011010] and creates a variable endarray, which in turn becomes [1 0 1 1 0 1 0]. When I implemented this piece of code I didn't quite know how it functioned, and it wasn't explained on the page where I found it, so I decided to go back to it later. Unfortunately I still haven't figured it out. I can't wrap my head around the combinations of sprintf, %d, and the -'0'.

Any help with understanding these two lines would be greatly appreciated.

[Pal Szabo]

I recommend to replace "Help with a piece of code" with something more meaningful

Answer 1

[Pal Szabo]

array3 is an integer. Sprintf needs to no that it is in decimal point notation, that's why you need the %d. More info: https://uk.mathworks.com/help/matlab/matlab_prog/formatting-strings.html. Strings in matlab are basically chain of chars. By subtractring -'0', you are basically subtracting 0 (decimal notation) from the ASCII values of the chars within the string. Executing an operation on each char within the chain of chars (aka on the string) gives a result of individual chars, since the operation only valid on individual chars, not on the string as a whole. Try this for example:

 array3 = [1011010]
 v = sprintf('%d', array3)
 endarray = v - '0' - 'd'

You get

-99  -100   -99   -99  -100   -99  -100

as result. 'd' is the ASCII character with decimal value 100. https://en.wikipedia.org/wiki/ASCII

You get the same result if define endarray like this:

    endarray = v - '0' - 100

Here 100 is an integer, not a chain of chars.

Sub in different values for 'd': the results are consistent with the ASCII table.

Hope this helps.

EDIT: I see you added a tag 'binary'. I do not think array3 is binary, just because it has only ones and zeros, it is pretty much a decimal value. Just like 8+2=10, 10 is not binary.

[José-Luis]

array3 is an integer. Sprintf needs to no that it is in decimal point notation, that's why you need the %d.

How do you figure that?

 sprintf('%d',0.5)

[Pal Szabo]

Okay you are right, I may be confusing the meaning of the expressions "decimal point" and "base 10". If I say

array3 is an integer. Sprintf needs to no that it is a number in base 10, that's why you need the %d.

Is this right?

[José-Luis]

Looks like array3 is a scalar and not a logical array.

Answer 2

[José-Luis]

Generating a "binary" (logical) array:

 a = rand(10,1) > 0.5;

Transforming the binary array into a string. v is a character array.

 v = sprintf('%d', a)

Transforming the string into a numeric array:

 endarray = v - '0'

Matlab does implicit conversions. When you do arithmetic operation with characters, it transforms them into double and then performs the operations.

 '0' - 48

Please note that all that is unnecessary if you want an array of doubles from a logical array. You could just have:

 endarray = double(a)

[Guillaume]

The starting point is not a logical array but a binary number encoded as a decimal, e.g.

 a = 1011010;

Hence the trip through a char array to get the digits of that decimal number.

[José-Luis]

Thanks. I was wrong but in essence sort of right.

Definitely maybe.