Hi guys. I need help splitting a number into its individual parts and then add them. E.g. the number would be 1994 = 1 + 9 + 9 + 4 = 23

I don't want the number to turn a scalar into an array eg x = 1994 = 1 9 9 4 I want it the scalar x = 1994 to split into multiple scalars. I hope this makes sense and your help will be much appreciated

Answer 1

[John]

When you say you do not want the number to turn to a scalar, I think what you are saying is you don't want to convert the scalar number x = 1994 into a vector v = [1 9 9 4].

If you are allowed to use string functions and are loose on your restriction, consider this:

x = 1994
%Convert x = 1994 to a vector of characters
a = num2str(x); %a now holds ['1' '9' '9' '4']

%Go through each of the elements in the vector, a, convert them to numbers and add them up
sum = 0;
for i = 1:size(a, 2)
sum = sum + str2num(a(i));
end

%sum now contains the sum of the individual digits

But this seems like a typical undergraduate homework problem :-) for a comp. sci./electrical enginering course :-) and the string approach above is unlikely to be the proper solution. I hope no one else provides the mathematical solution to this :-) as this is not a MATLAB question.

As a hint, consider the significance of the position of the individual digits in the number. We call them the one's, ten's, hundred's, and thousand's position for a reason :-)

[tyler brecht]

Wow u are wise :), thanks a lot John this is exactly what I was looking for:). I'm actually doing a mechanical engineering course, but this solution will help me a lot in completing my assignment, which contains a if function and while loop

[John]

A glimpse from the mathematical vantage point:

x = 1994;
a = 1994 / 1000; 
a = floor(a); %a = 1, ..cough.. the thousand's position

b = x - a * 1000; % b = 994
b = b / 100;
b = floor(b); % b = 9, ..cough.. the hundred's position

None of the variables above are vectors.

Answer 2

[Guillaume]

n =  1994; 
num2str(n) - '0'

[tyler brecht]

Thank you :)

[CHAIYUT CHAROENPHON]

work perfectly.

[HARSHA HN]

Legendary answer!

[Vo Luan]

Best answer, Thank you!

[andrea]

Can anyone give me an hint on why it works ? thank you

[Jan]

@andrea: num2str converts a number to the corresponding CHAR vector:

n =  1994; 
num2str(n)   % '1994'

If you subtract another CHAR from this vector, this is done elementwise in Matlab:

'1994' - '0'  % Is the same as:
['1', '9', '9', '4'] - '0'
% This is calculated elementwise:
['1' - '0', '9' - '0', '9' - '0', '4' - '0']

If CHARs appear as input to a numerical operation, their ASCII values are used. So this is converted to:

[49 - 48, 57 - 48, 57 - 48, 52 - 48]

which is:

[1, 9, 9, 4]

Answer 3

[Jan]

N = 1994;
m = floor(log10(N));
D = mod(floor(N ./ 10 .^ (m:-1:0)), 10);

>> D = [1, 9, 9, 4]

[Tejas Mahajan]

Hi Jan,

Can you please explain this code please.

[John D'Errico]

@Tejas Mahajan - easy enough. But you should make the effort yourself. What, for example does this do?

10 .^ (m:-1:0)

Now, what would happen when you do this?

N ./ 10 .^ (m:-1:0)

Now add one more layer around that?

floor(N ./ 10 .^ (m:-1:0))

Try that part for 1994. Now, look at the last step in his code.

mod(floor(N ./ 10 .^ (m:-1:0)), 10);

What did that do?

When you don't understand a piece of code, break it apart. Start in the middle, then work outwards, one part at a time until you do see what it does. You won't learn otherwise.

Answer 4

[per isakson]

A one-liner with a lot of Matlab

    >> sum( arrayfun( @(a) str2double(a), num2str( 1994 ) ) )
    ans =
        23

or even more matlab-ish

    >> sum( arrayfun( @str2double, num2str( 1994 ) ) )
    ans =
        23

This is essential the same as John's solution with the for-loop replaced by the function, arrayfun

[Guillaume]

Or my solution is a lot more straightforward

sum(num2str(n)-'0');

[per isakson]

Straightforward to those who

• are familiar with ascii-numbers
• understand that Matlab automagically returns numbers as the result of a difference between two strings (minus is defined for strings?)

[John]

This would make a great MATLAB Cody challenge

[Guillaume]

Oh, it's been used in a lot of cody challenges.

[per isakson]

'ABC'-'A' Considered Harmful

[Guillaume]

Well, as the accepted answer states, it's the most efficient way of converting a string into individual numbers, and the way you'd do it in a number of other languages (at least the C based one).

[per isakson]

With Matlab, to explicitly convert to numeric before doing arithmetic is faster.

[tyler brecht]

Yes I see your solution is more efficient and more advanced, I would use it but I need to get to understand the arrayfun function first before using it

[Star Strider]

arrayfun

[per isakson]

Fewer lines of code is good, but one should only use code that one understands and is able to take responsibility for.

Answer 5

[Joachim Posselt]

yyyy = 1994;

% dig = digits extract // Ziffern extrahieren - mit Mathe, nicht mit Strings!!

dig_t = floor (yyyy / 1000); % tausender // thousands

dig_h = yyyy - dig_t * 1000;

dig_h = floor (dig_h / 100); % hunderter // hundreds

dig_z = yyyy - dig_t * 1000 - dig_h*100;

dig_z = floor (dig_z / 10); % zehner // ten

dig_e = yyyy - dig_t * 1000 - dig_h*100 -dig_z*10;

dig_e = floor (dig_e / 1); % einer // ones