How to replace 1 column in table

Hello!

I have a NaN table (100x200), lets call it A, and a large dataset with first column being participants ID (eg 123AJH), lets call this B. I want to find the unique participant ID in B (:,1) (eg there are 100 unique IDs as many of them are repeated) and replace the unique IDs as the first column of A. However, the result is 1,2,...100 (the number of unique ID) rather than the ID itself (123AJH).

Anyone knows how to replace 1st column of A with the column of unique IDs found in B (123AJH; 232AJH, ...) ?

Much appreciated thank you. The code I wrote is below:

A (:,1) = unique (B(:,1));

[Dyuman Joshi]

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Answer 1

[Sachin]

Hi Cside,

I understand that you want to replace 1 column in table.

Following steps might be helpful to you :

1. First find the unique values in Table B using "unique".
2. Find the count of those unique values using function "length".
3. Create a vector representation from 1 to count.
4. Then assign the values to the Table A.

dummyTableA = [2,3;3,4;4,5]; %dummy table a
Age = [38;43;38;40;38];
unique_Age = unique(Age)  % find the unique values

unique_Age = 3×1

38 40 43

count_uniqueAge = length(unique_Age)  % find the count of unique values

count_uniqueAge = 3

unique_ids = [1:1:count_uniqueAge]  % create a vector 

unique_ids = 1×3

1 2 3

dummyTableA

dummyTableA = 3×2

2 3 3 4 4 5

dummyTableA(:,1) = unique_ids;  % update the value of column 1 in table A
dummyTableA  

dummyTableA = 3×2

1 3 2 4 3 5

You can refer the following MATLAB Documentations for more information about above functions :

https://in.mathworks.com/help/matlab/ref/double.unique.html

https://in.mathworks.com/help/matlab/ref/colon.html

Thanks

Sachin

[Cside]

Hi Sachin,

Thank you for your reply. I would like the first column of dummyTableA to be 38;40;43 instead, not the number of unique IDs

[Sachin]

Hi Cside,

Then you can simply do :

dummyTableA(:,1) = unique_Age;