Home/ Questions/Quick handling of the: ''Argument to dynamic structure reference must evaluate to a valid field name'' error.
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Arthur Thomas
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Asked: 2022-05-18T18:31:50+00:00 In:

Quick handling of the: ”Argument to dynamic structure reference must evaluate to a valid field name” error.

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Hi developer experts, I have a small but frustrating use case, and so far, I couldn’t get my head around this problem & ideal solution. I am running my command and facing one problem with the argument to dynamic structure reference must evaluate to a valid field name. Below is the command I used:

spectData{1} = 
 
 data: [256x26 double]
 textdata: {1x26 cell}
 colheaders: {1x26 cell}
 Row: [256x1 double]
 Col: [256x1 double]
 Cho: [256x1 double]
 Cho0x25SD: [256x1 double]
 Cho0x2FCit: [256x1 double]
 PCho: [256x1 double]
 PCho0x25SD: [256x1 double]
SDdata = spectData{sliceNum - firstSlice}.(MetabMapSDString);

When I run it, I get the following error:

Argument to dynamic structure reference must evaluate to a valid field name.

I am looking forward to gaining some knowledge from all experts. Thank you, guys!

must evaluate to a valid field name
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2 Answers

  1. Best Answer
    Expert

    The cause:

    You got this error because instead of passing a string, you mistakenly sent a cell array. Literal strings, on the other hand, are of the char array type. This error also appears in below program:

    fields = {'foo', 'bar'}
s = struct('foo', 23, 'bar', pi)

for f = fields
disp(f)
s.(f) = 0
end

    Solution:

    You should check your field name, for example with whos and use f = char(f) in your program.

    • 0

  2. Matlab refers to a string as a cell. Literal strings are of type array. They print differently. A cell string prints as 

    ans =

 'abc'

    While a regular char array prints, 

    ans = 
abc

    The difference between the two functions is cellstr and char, which convert char arrays to strings.

    In your case, char(MetabMapSDString) should be used as the dynamic struct reference.

    • 20

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