Ignoring empty arrays when using arrayfun on a structure?

Question

bio lim 2015-8-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/234045-ignoring-empty-arrays-when-using-arrayfun-on-a-structure

评论： bio lim 2015-8-16

I have 1x2269 structure with 20 fields called data. I am trying to extract with a condition using arrayfun.

west_east = arrayfun(@(n) 110 >= data(n).TTA(1) & data(n).TTA(1)   >= 70, 1 : length(data));
data = data(west_east);

The problem is that some of the arrays in my structure are empty. When I run the code, I am getting the error

Attempted to access data2.TTA(1); index out of bounds because
numel(data2.TTA)=0.

I understand that this is due to having empty cells in my structure such as

data2(9)
ans = 
                   type: 'B738'
                   time: [0x1 double]
                    lat: [0x1 double]
                    lng: [0x1 double]
               altitude: [0x1 double]
    selected_altititude: [0x1 double]
                    BPS: [0x1 double]
                     RA: [0x1 double]
                    TTA: [0x1 double]
                     GS: [0x1 double]
                    TAR: [0x1 double]
                    TAS: [0x1 double]
                heading: [0x1 double]
                    IAS: [0x1 double]
                   Mach: [0x1 double]
                    BAR: [0x1 double]
                    IVV: [0x1 double]
                   wind: [0x1 double]
              real_time: []
       instantaneous_GS: []
           displacement: []

How can I adjust my code to get what I want? Thanks.

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Answer 1

David Young 2015-8-16

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https://ww2.mathworks.cn/matlabcentral/answers/234045-ignoring-empty-arrays-when-using-arrayfun-on-a-structure#answer_189458

在 MATLAB Online 中打开

Try this (not yet tested):

west_east = arrayfun(@(d) ~isempty(d.TTA) && 110 >= d.TTA(1) && d.TTA(1) >= 70, data);
data = data(west_east);

Notes:

I assume that the elements with empty arrays should be rejected like the ones that fail the test.
You don't need to apply arrayfun to an array of indices then index the array within the anonymous function. You just apply arrayfun to the array directly, and the anonymous function is applied to each element in turn.
When combining logical scalars (as here) it's more efficient to use && rather than &. In this case it's essential, in order to avoid accessing the TTA field if it's empty.