Help with this problem

Hi. I am trying to solve this problem:

Write a function called simple_stats that takes a matrix N as an input and returns the matrix S as the output. S has the same number of rows as N. Each element of the first column of S contains the mean of the corresponding row of N. Similarly, the second column contains the median values; while the third column has the minimums. Finally, each element of the fourth column of S is equal to the maximum value of given row of N.

I wrote

function S = simple_stats(N)
    S = [mean(N,1); median(N,2); min(N,[],3); max(N,[],4)]

but this is not working. any suggestions?

Answer 1

[Stephen23]

Your dimensions were all messed up: note that , is used to concatenate the columns horizontally (you used ; which concatenates vertically), and you tried to specify the output column as the input argument to each function (but this should simply be the dimension to work along on the input matrix):

function S = simple_stats(N)
S = [mean(N,2),median(N,2),min(N,[],2),max(N,[],2)];

and tested:

>> X = randi(9,7)
X =
     8     5     8     1     6     8     7
     9     9     2     8     2     7     8
     2     9     4     9     7     3     2
     9     2     9     7     1     9     5
     6     9     8     7     3     1     5
     1     9     9     7     1     4     6
     3     5     6     4     1     4     7
>> simple_stats(X)
ans =
       6.1429            7            1            8
       6.4286            8            2            9
       5.1429            4            2            9
            6            7            1            9
       5.5714            6            1            9
       5.2857            6            1            9
       4.2857            4            1            7

Hint: don't just write code and hope that it works. Write and check it as you write it. Check every line and every command, that it is doing exactly what you need it to do. Beginners often seem to think that a command is doing something, but never even bother to check. You could easily have run those functions (mean, etc) in the command windows with small matrix, and discovered that the output was not as you expected...

Also, learn to read the documentation. That would also have told you that you were using them incorrectly.

Answer 2

[fenam sogani]

function S = simple_stats(N) S = [mean(N,2),median(N,2),min(N,[],2),max(N,[],2)];

what meaning of 2 here

[Stephen23]

Did you read the mean, median, min, and max documentation? The documentation clearly explains what all of the inputs mean.

Answer 3

[Liban Abu]

one way i approached this is

a = mean(N,2);
b = median(N,2);
c = min(N,[],2);
d= max(N, [],2);
S = [a b c d]

i dont know if this makes sense

[Stephen23]

That is what I showed in my answer, just with several intermediate variables rather than on one line: if you like the clarity of this, go for it!

Answer 4

[ossai rex]

please what those [] and 2 stand for in the command line