How do I change a specific row of a table that I manually filtered out?

I have a table of > 1 million rows. I need to find a specific row in this table and update 2 columns. I can find the row by filtering by 3 columns:

filter = (Table.A == "a" & Table.B == "b" & Table.C == "c");
row = Table(filter, : );

Here, “row” is the correctly filtered. I then assign new values to the row's elements by using the following commands: 

row.D = “d”;
row.E = “e”

One would assume that the 'D' and 'E' elements of the row are now updated , but when I print out the table, they still show the old values.

I was able to successfully edit the table by iterating through the > 1 million rows, and calling the list of updates (50,000 lines long). But this procedure takes hours. How can I efficiently achieve this workflow?

Answer 1

[MathWorks Support Team]

The issue here is that "row" is not a pointer to the row in the table. It is a copy of the value there. After updating "row" to the desired values, you need to directly set the table's row by doing something like this:

table(filter, :) = row;

Here's a complete example of filtering the rows and setting the table correctly:

%% Generate a table
A = ["a" "a" "b" "x" "a" "a"]';  B = ["g" "b" "b" "f" "x" "b"]'; C = ["c" "c" "f" "c" "c" "e"]';
D = repmat(string, 1, 6)'; E = repmat(string, 1, 6)';
T = table(A, B, C, D, E);

%% Filter and replace the data
filter = (T.A == "a" & T.B == "b" & T.C == "c");
row = T(filter, :);
row.D = "d";
row.E = "e";
T(filter, :) = row; % Try commenting and uncommenting this line to see the difference in T