Test for existance of column in table Matlab

Question

I Have the following table, T:

      Hold       Min    Max 
    _________    ___    ____

     0.039248    0      0.05
     0.041935    0      0.05
     0.012797    0      0.05
    0.0098958    0      0.05
     0.014655    0      0.05

How can I test if a column in a table exists? For example isfield(T,'Hold') returns 0. Exist, isstruct also do not work. I would need the test to simply return a true or false result.

sco1 · Answer 1 · 2017-03-22T11:09:19.197

5

See: Table Properties

For example:

LastName = {'Smith';'Johnson';'Williams';'Jones';'Brown'};
Age = [38;43;38;40;49];
Height = [71;69;64;67;64];
Weight = [176;163;131;133;119];
BloodPressure = [124 93; 109 77; 125 83; 117 75; 122 80];

T = table(Age,Height,Weight,BloodPressure,...
    'RowNames',LastName);

myquery = 'Age';
columnexists = ismember(myquery, T.Properties.VariableNames)

Returns:

columnexists =

     1

edited Mar 22 '17 at 11:09

answered Sep 18 '15 at 15:42

sco1

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You can use `ismember` in last line `columnexists =ismember(myquery, T.Properties.VariableNames)` – Mohsen Nosratinia Sep 18 '15 at 16:08

score 4 · Accepted Answer · answered Sep 18 '15 at 15:49

4

You can convert to struct and then use isfield:

isfield(table2struct(T),'Hold')

answered Sep 18 '15 at 15:49

Luis Mendo

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This might be a performance hit for larger data sets. Probably better to use [solution by excaza](http://stackoverflow.com/a/32656035/388664) (with Mohsen's comment). – Nikola Malešević Aug 17 '16 at 11:33

score 0 · Answer 3 · answered Sep 01 '16 at 09:36

ismember('myFieldName', myTable.Properties.VariableNames)

or put into a nice function:

function hasField = tablehasfield(t, fieldName)
    hasField = ismember(fieldName, t.Properties.VariableNames);
end

How to use the function:

x = [2 5 3];
t = table(x); % create table with a field called 'x'

if tablehasfield(t, 'x')
    % do something
end

score 0 · Answer 4 · answered May 10 '17 at 12:50

The usual tests cause a script to crash if the subject (Table in this case) doesn't exist: isfield(), ismember(), isempty() these all have that problem.

exist() checks without crashing, but only works on the table, so you still need checks for the existence of the column, and you asked whether there was data in the column:

%define table
Hold = [0.039248 0.041935 0.012797 0.0098958 0.014655]';
Min=[0 0 0 0 0]';
Max = [0.05 0.05 0.05 0.05 0.05]';
T = table(Hold,Min,Max);

%test table
if exist('T') 
   myquery = 'Max';
   if ismember(myquery, T.Properties.VariableNames)
       col = find(strcmp(myquery, T.Properties.VariableNames));
       T(:,col)
   end
 end

...and displays it as a bonus

Test for existance of column in table Matlab

4 Answers4