How can I assign a variable to a string?

I have a mat file containing a table one column with numbers from 1 to 50, I just want to assign avariable to first column an than apply this:

tf = ismember(M, [7; 8; 9]);
idx = find(diff(tf)>0)+1+(0:12);
answer = reshape(M(idx).', [], 1)

If I put

M = [1 2 3 4...49 50] 

and then

tf = ismember(M, [7; 8; 9]);
idx = find(diff(tf)>0)+1+(0:12);
answer = reshape(M(idx).', [], 1) 

I have the correct results that display only the numbers after 9 but I want to exclude the M = [1 2 3 4...49 50] and to assign a variable to entire column because my numbers are always different except 7,8,9

I tried this

M = T(:,:); 

where T is the table from mat file but:

Error using table/ismember (line 27)

A and B must both be tables.

If I put directly:

 tf = ismember(X, [7; 8; 9]); %X is table from mat file
idx = find(diff(tf)>0)+1+(0:12);
vals = reshape(X(idx).', [], 1);

I get this error :

Error using +

Matrix dimensions must agree.

Thanks

[Image Analyst]

You forgot to format your code and attach your mat file. I formatted it for you but I can't attach your mat file for you.

[Cristian Martin]

load('simplu.mat');

M = T(:,:);

tf = ismember(M, [7; 8; 9]);

idx = find(diff(tf)>0)+1+(0:12);

answer = reshape(M(idx).', [], 1)

I attached the mat file (T is the table from mat file) still dont get it what I need to format...

Answer 1

[dpb]

>> whos -file simplu
  Name      Size            Bytes  Class    Attributes

  T          -               1440  table              

>> load simplu
>> whos T
  Name       Size            Bytes  Class    Attributes

  T         50x1              1440  table              

>> T(1:5,:)
ans =
  5×1 table
    Var1
    ____
    1.00
    2.00
    3.00
    4.00
    5.00
>> tf=ismember(T,[7:9]);
Error using tabular/ismember (line 37)
A and B must both be tables, or both be timetables. 
>> tf=ismember(T.Var1,[7:9]);
>> 

Error is correct; T is a table and [7;8;9] is a vector of double...never the twain shall meet.

As the second shows, you need to reference the variable in the table.

ADDENDUM:

Error using tabular/ismember (line 37)
A and B must both be tables, or both be timetables. 

The error message is correct, as far as it goes. It was written specifically for the case of the tabular/ismember function; what it neglects to point out is that both could be numeric and the alternate ismember method would work as well...