MATLAB: How to index within a structure

data manipulationdata storagefunctionalityindexindexingindicesMATLAB and Simulink Student Suitemeanstructure

I am trying to take the mean of a structure.field column's number for multiple patients in a structure and store it for a plot of all the means later.
ShiftData(1).meanX = mean([patient(applicablepatients).Xtumorshift(1)])
This causes an error: Expected one output from a curly brace or dot indexing expression, but there were 65 results.
The MATLAB Help Documentation " Access Data in a Structure Array" states, "Note: You can index into part of a field only when you refer to a single element of a structure array. MATLAB® does not support statements such as S(1:2).X(1:50,1:80), which attempt to index into a field for multiple elements of the structure."
It appears that what I am trying to do is not supported. Am I understanding this correctly? Why is it not supported? Must I first store the data in a vector and then take the mean of that vector? Why?
Here is the contents (ID changed) of the second element in structure 'patient', patient(2):
             ID: 999999
     Xboneshift: [1x21 double]
     Yboneshift: [1x21 double]
     Zboneshift: [1x21 double]
    Xtumorshift: [1x21 double]
    Ytumorshift: [1x21 double]
    Ztumorshift: [1x21 double]
       TableLat: [1x21 double]
      TableLong: [1x21 double]
      TableVert: [1x21 double]
         TxDate: {1x21 cell}
       FxNumber: [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21]
(Is the correct terminology "structure(element).field"?)

Best Answer

Instead of indexing within an array stored in a structure element, I sorted the structure elements' arrays into a new structure, essentially David Sanchez's suggestion.
One can index into a structure field the same way one indexes into an array, if that field is an array. Working with ulrickls's dicomrt2matlab files, a DICOM-RT contour can be visualized:
scatter3(contours(9).Points(:,1),contours(9).Points(:,2),contours(9).Points(:,3))
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