How to access nested array value?

Matlab: loading and editing an array/structure confusion?

• I have a matlab coding question involving editing arrays from a matlab file. The overall problem is that I can't figure out how to work with this matlab array. I have an array that is 1100841x4 double (pulled from some data that was collected), and I want to change all values in the 1st column into 0's unless they are greater than 5. I was planning on using a "for" loop with a nested "if" statement to search out the values and change them. I have been using the "load" function to access the file and assign it to a variable and the "whos" function defines the newly loaded variable as a "1x1 structure". Is it that I (a) should be using a different loading function, or is (b) there a different way to use the load function that I have missed? Otherwise, how do I single out or direct my "for" loop and "if" statement(s) to that one column and not the entire array? google, mathworks, and matlab's "help" function haven't gotten me anywhere. I'm at a complete loss. p.s. excel isn't able to work with the sheer amount of data and says so in an error message Thank you very much for any time anyone spends on helping me figure out this issue.

• Answer:

  Is your data file just plain text (i.e., just a table of numbers)? Or is it a binary .mat file? If the former, then the statement myarray = load('/path/to/my/file'); should create "myarray" as a 1100841x4 array, not a structure. I suspect the file might be a binary data structure instead, in which case if you just do load('/path/to/my/file'); then the variable(s) of interest should be loaded into your workspace. If you're still getting a 1x1 structure, then try typing the name of the variable, not followed by a semicolon, and see if one of the structure fields contains the array you want. In any case, assuming myarray contains your data, a fast way to manipulate it the way you want is by using logical arrays. A few basics: myarray(:,1) is the first column of data. So if you do myarray(:,1) = 0; this will set all values of the first column to zero. If you do should_set_to_zero = myarray(:,1)<=5; then this will create an array of boolean values (0's and 1's) of the same size as the first column of your data, where there is a 0 if your data is greater than 5, and a 1 if your data is less than or equal to 5. Then, you can do myarray(should_set_to_zero,1) = 0; This will set to zero all the first column entries that are less than or equal to 5. A for loop is slower, but simpler to understand. For example: for i = 1:size(myarray,1) if (myarray(i,1)<=5) myarray(i,1) = 0; end end Hope that helps. For more detail, try http://www.mathworks.com/help/techdoc/ref/colon.html http://www.mathworks.com/help/techdoc/math/f1-85462.html#bq7egb6-1