How to exclude certain rows and columns based on a column value?

Dear all,

Attached you find a data file called "a" that has 30 rows and 24 columns. What I call "a trial" represents 1 row of "a" that includes all 24 columns, i.e. a trial refers to a(1,:).

I'm trying to create a variable called "b" that includes all trials of "a" where column 24 of "a" contains numbers <2560.

My first solution was

b= a(a(:,24)<2560)

Yet, this solution doesn't render the results I expect.

In order to unpack the problem, I've tried to create a new variable "c" that has only 1 column instead of 24 (like "a" does).

c= [2345; 2780; 345; 2150; 2908; 451]

Now, if I create a variable "d" that includes all rows in "c" that are <2560, the solution I used on the variable "b" above works.

d=c(c<2560)

This makes me think the problem lies with the fact that "a" has 24 columns (instead of 1 column, like "c" has). I'm trying to see what I'm missing, but I can't find an answer. Would any of you please be so kind as to help me out?

With gratitude,

Bianca

Answer 1

[Birdman]

Firstly, at your first line of code, you started checking from the beginning of a. Instead, you should be checking the 23rd column of a

b= a(:,a(:,23)<2560)

Also, you are missing the fact that there is no element in the 23rd column of a that is less than 2560. Therefore that line will return empty.

[Bianca Elena Ivanof]

Thank you for taking the time to help me out.

I've now replaced the former attachment with another variable "a" that contains 24 columns. There are quite a few elements in the 24th column <2560. I've tried out your line of code above:

b= a(:,a(:,24)<2560)

, yet it's saying that "index exceeds matrix dimensions".

Again, I'm trying to deconstruct the problem - this one:

a(:,24)<2560

works.

Do you happen to be able to please help me further by any chance?

Bianca

[Ameer Hamza]

I guess Birdman mistyped the order of subscripts in his answer. Correct command is

b = a(a(:,24)<2560,:);

[Bianca Elena Ivanof]

Perfect. It works now. Thank you both very much.

Stay safe,

Bianca