Iterating through struct fieldnames in MATLAB

Question

My question is easily summarized as   Why does the following not work    teststruct   struct  a  3  b  5  c  9   fields   fieldnames teststruct   for i 1 numel fields    fields i    teststruct  fields i   end   output   ans    a       Argument to dynamic structure reference must evaluate to a valid field name    Especially since teststruct   a   does work  And fields i  prints out ans    a    I can t get my head around it

User · Answer

Your fns is a cellstr array  You need to index in to it with    instead of    to get the single string out as char   fns i  teststruct  fns i     Indexing in to it with    returns a 1-long cellstr array  which isn t the same format as the char array that the    name   dynamic field reference wants  The formatting  especially in the display output  can be confusing  To see the difference  try this   name as char    a  name as cellstr     a

User · Answer

You can use the for each toolbox from http   www mathworks com matlabcentral fileexchange 48729-for-each       gt  gt  signal signal    sin    1x1x25 cell    1x1x25 cell   cos    1x1x25 cell    1x1x25 cell     gt  gt  each fieldnames signal   ans    CellIterator with properties   NumberOfIterations  2 0000e 000   Usage   for bridge   each fieldnames signal      signal  bridge    rand 10   end   I like it very much  Credit of course go to Jeremy Hughes who developed the toolbox

User · Answer

Since fields or fns are cell arrays  you have to index with curly brackets    in order to access the contents of the cell  i e  the string    Note that instead of looping over a number  you can also loop over fields directly  making use of a neat Matlab features that lets you loop through any array  The iteration variable takes on the value of each column of the array   teststruct   struct  a  3  b  5  c  9   fields   fieldnames teststruct   for fn fields    fn      since fn is a 1-by-1 cell array  you still need to index into it  unfortunately   teststruct  fn 1   end

User · Answer

You have to use curly braces      to access fields  since the fieldnames function returns a cell array of strings   for i   1 numel fields    teststruct  fields i   end   Using parentheses to access data in your cell array will just return another cell array  which is displayed differently from a character array    gt  gt  fields 1     Get the first cell of the cell array  ans          a          This is how the 1-element cell array is displayed   gt  gt  fields 1     Get the contents of the first cell of the cell array  ans    a               This is how the single character is displayed

[matlab] Iterating through struct fieldnames in MATLAB

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