How to fill-in a smaller table into a larger (empty) table with a sorted variable?

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I have extracted smaller tables from large data for further analysis. After extraction, the table needs to be sorted and has missing values. To address these two, I have made an empty table with the sorted variable (the channel 'variable'). I just want to shift the values of the extracted tables into the ref_table (empty table).
I have put a partial code for working below:
clc
clear all
close all
load("del.mat")
names = {T1,T2};
for i = 1:2
ref_table = DummyTable;
tab = names{i};
% 1. tab sorted in ascending 'channel' variable and filled-in the reftable
% 2. In second loop, the values of channel 5 are missing, and should be
% left as nan.
end
I can visually explain what I want to do in excel sheet screenshots below:
The red table is sortd first and then filled in the green table as below:
The missing values should be shown as nan, as shown in the next picture
Thank you.

Accepted Answer

Cris LaPierre
Cris LaPierre on 14 Oct 2024
Joining doesn't appear to selectively replace values in one table. With the assumption that all channels only appear once in the small tables, here's an approach that doesn't use loops.
load del.mat
[~,r] = ismember(T1.channel,DummyTable.channel)
r = 8×1
1 2 7 3 4 8 5 6
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
T1new = DummyTable;
T1new(r,:) = T1
T1new = 8x5 table
Clock tot channel TOA Ampdb ______________ ______ _______ ______ _____ {["10:32:14"]} 14.505 1 14.505 88 {["10:32:14"]} 14.505 2 14.505 80 {["10:32:14"]} 14.505 3 14.505 58 {["10:32:14"]} 14.505 4 14.505 70 {["10:32:14"]} 14.505 5 14.506 47 {["10:32:14"]} 14.505 6 14.506 58 {["10:32:14"]} 14.505 7 14.505 75 {["10:32:14"]} 14.505 8 14.505 64
[~,r] = ismember(T2.channel,DummyTable.channel)
r = 7×1
2 1 7 3 4 8 6
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
T2new = DummyTable;
T2new(r,:) = T2
T2new = 8x5 table
Clock tot channel TOA Ampdb ______________ ______ _______ ______ _____ {["10:32:31"]} 31.962 1 31.962 74 {["10:32:31"]} 31.962 2 31.962 85 {["10:32:31"]} 31.962 3 31.962 55 {["10:32:31"]} 31.962 4 31.962 66 {0x0 double } NaN 5 NaN NaN {["10:32:31"]} 31.962 6 31.962 53 {["10:32:31"]} 31.962 7 31.962 69 {["10:32:31"]} 31.962 8 31.962 57
  1 Comment
Muha
Muha on 15 Oct 2024
Dear @Cris LaPierre this is very concise. In two lines I can populate the local table into dummy table as I have already assigned dummy table at the start of loop. Thank you for an efficient solution.

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More Answers (1)

Rahul
Rahul on 15 Oct 2024
Hi @Muha,
I believe you are trying to take extracted tables (T1, T2) and transfer their values into a reference table (ref_table) sorted by the 'channel' variable, while handling missing values (channels that are missing should remain NaN), here's how you can modify your code:
  1. Sort the extracted table (tab) by the 'channel' variable.
  2. Match the rows of the sorted table (tab) with the 'channel' values of the reference table (ref_table).
  3. Transfer the values from the extracted table into the correct positions in the reference table.
clc
clear all
close all
% Load the data (del.mat contains T1, T2, and DummyTable)
load("del.mat")
% Names of the extracted tables
names = {T1, T2};
for i = 1:2
% Reference empty table (DummyTable)
ref_table = DummyTable;
% Current extracted table (T1 or T2)
tab = names{i};
% Sort the extracted table by the 'channel' variable in ascending order
tab = sortrows(tab, 'channel');
% Now, match 'channel' values of 'tab' with 'ref_table'
for j = 1:height(tab)
% Find the index of the current 'channel' in the ref_table
channel_value = tab.channel(j);
% Find the row in the ref_table where the 'channel' matches
idx = find(ref_table.channel == channel_value);
% If a matching channel is found, transfer the data
if ~isempty(idx)
% Transfer the corresponding data from tab to ref_table
ref_table(idx, :) = tab(j, :);
end
end
% Display the updated ref_table for the current table
disp(['Updated ref_table for T', num2str(i)]);
disp(ref_table);
end
For more information regarding the functions used in the given code snippet, refer to the folllowing documentation links:
Best!
  2 Comments
Muha
Muha on 14 Oct 2024
Moved: Cris LaPierre on 15 Oct 2024
Well, it works. Thank you. I thought there is some sort of outer/inner join function to sort things out. But this is great. I will use this as a function. Thank you for such a detailed explanation. If you put your solution in the answer, I will accept the answer. Thank you

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