Styjun

I am working currently with matlab and I try to extract some data from a struct that I have, but it seems it is not as easy I thought it would be.

structExample = 1x100000
fieldnames(structExample)

ans =

 6×1 cell array

 'a'
 'b'
 'c'
 'd'
 'e'
 'f'

I am interested in the values saved in field 'b'.
When I type structExample.b it prints out all the values, but when I do

values = structExample.b

It only saves the first values ([1.2,5.33]) . 'b' has double values for example

[1.2,5.33], 1x86double, 1x120double ...

My aim is to be able to plot them with cdfplot()

So I thought maybe iterate over all values in the field and save them in a separate array. But I don't know how to iterate through it, since structExample.b only takes the first values. Any ideas?

Edit:

structExample.b(3) returns

Expected one output from a curly brace or dot indexing expression, but
there were 41817 results.

When you access a field of a structure array, it returns a comma-separated list of values. By default, only the first value in a list will be assigned to a single variable. If you want to capture all of these values, you have to collect them using [] (for a normal array) or (for a cell array). Since you are dealing with different-sized sets of data in each structure, you will need to use a cell array:

values = structExample.b;

So, values1 will contain [1.2,5.33], values2 will contain 1x86 double, etc..

For the case where you want to iterate over the structure array, you have to index array elements and fields in the correct order. You should index the element first (which gives you a single structure element from the array), then index the field you want:

value = structExample(3).b; % Field b of the third array element

For the additional case where you want to collect a field from an indexed subset of elements in your structure array, you have to combine the indexing and collection schemes from above. For example:

values = structExample([structExample.a] == 1).b;

This will collect all a field values from structExample into an array, find a logical index for where they equal 1, index the structExample array with that logical array, then collect the values of field b from that subarray and place them in a cell array.