tables remove one field

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Patrick Brown
Patrick Brown on 23 Feb 2017
Answered: Peter Perkins on 28 Feb 2017
I have three fields in a table
T.Position= 'No' '10' '20'
T.Velocity= 'No' '10' '60'
T.Acceleration= 'No' 'No' 'No'
then I want to eliminate the field that have all values 'No' which is only Acceleration
How I can do it??

Answers (3)

Chibuzo Nnonyelu
Chibuzo Nnonyelu on 23 Feb 2017
Goes through each column and deletes a column if the number of 'No' found in the column is equal to the height of the table.
for m = 1:width(T)
if length(strfind(strjoin(table2cell(T(:, m))), 'No') ) == height(T)
% delete the column;
T(:, m) = [];
  1 Comment
Jan on 23 Feb 2017
Edited: Jan on 23 Feb 2017
if all(strcmp('No', table2cell(T(:, m))))
I cannot try this currently, but would this work also:
if all(strcmp('No', T{:, m}))

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Patrick Brown
Patrick Brown on 23 Feb 2017
It does not work well because you have this error Variable index exceeds table dimensions.
maybe because you are changing the width of T when you delete columns

Peter Perkins
Peter Perkins on 28 Feb 2017
I'll assume that your table looks like this:
>> t = table({'No'; 10; 20}, {'No'; 10; 60}, {'No'; 'No'; 'No'}, 'VariableNames',{'Position' 'Velocity' 'Acceleration'})
t =
Position Velocity Acceleration
________ ________ ____________
'No' 'No' 'No'
[10] [10] 'No'
[20] [60] 'No'
(which is not at all clear). How would you do this with any MATLAB array? The answer is essentially the same: loop over the variables in the table, deleting the ones that are all No's, and loop backwards so you're not deleting things out from under yourself. "dot-parens-index" dubscripting makes this almost identical to what you'd do for a double array.
for j = width(t):-1:1
if all(strcmp(t.(j),'No'))
t.(j) = [];
Another way is to use varfun to figure out what to delete, and then delete all at once.
toDeleteFun = @(x) all(strcmp(x,'No'));
toDelete = varfun(toDeleteFun,t,'OutputFormat','uniform')
t(:,toDelete) = [];
The terminology for tables is "variables", not "fields" or "columns".


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