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Neel Kulkarni il 23 Giu 2024 alle 13:19
Modificato: dpb il 24 Giu 2024 alle 15:56
Suppose I have a table, T:
A B C
1610
2520
3430
4345
526
6110
I want to subtract each entry in column C where the A and B values are flipped, and put this value into column D
For example, the first row (1, 6, 10) - the last row (6, 1, 10); (2, 5, 20) - (5, 2, 6) and so on
So D should be:
14
-15
15
-14
Thanks a lot!
Edit: (i) Flipped rows could occur anywhere in the table; (ii) there may be repeated values in Α and B
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John D'Errico il 23 Giu 2024 alle 13:38
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Modificato: John D'Errico il 23 Giu 2024 alle 13:39
Define "flipped". The exmple you show does not suggest what it might mean.
Torsten il 23 Giu 2024 alle 13:46
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M = [1610
2520
3430
4345
526
6110];
D = M(:,3)-flipud(M(:,3))
D = 6x1
0 14 -15 15 -14 0
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Neel Kulkarni il 23 Giu 2024 alle 13:52
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The first row has (A, B, C) as (1, 6, 10). The last row has the first two values flipped, i.e., (6, 1, 10). Similarly between the second and penultimate row the first two values are flipped: 2, 5, 20 and 5, 2, 6. I would like the code to identify such rows and subtract the C column values from each other (so 10-10 = 0; 20-6 = 14)
Image Analyst il 23 Giu 2024 alle 13:55
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Is the flipped row always at numRows-row+1, like 1 and 6, 2 and 5, 3 and 4, or might the "flipped row" occur anywhere, at any row?
Torsten il 23 Giu 2024 alle 14:01
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@Image Analyst
Seems it can occur anywhere - otherwise my suggested solution would work.
Neel Kulkarni il 23 Giu 2024 alle 14:05
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Modificato: Neel Kulkarni il 23 Giu 2024 alle 14:07
@Torsten thanks for your solution; indeed it works if the example is stuck to, but my actual, larger dataset is not as orderly unfortunately. The flipped rows occur anywhere, and there are repeated values in A and B columns as well (forgot to add this in the original question, have added it as an edit just now). The (A,B) couple itself is flipped, not merely that B is A flipped upside down. Apologies that the original question was not clear about this.
Torsten il 23 Giu 2024 alle 14:12
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Please give an example for
there are repeated values in A and B columns as well
and how this case is handled.
Neel Kulkarni il 23 Giu 2024 alle 14:25
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Modificato: Neel Kulkarni il 23 Giu 2024 alle 14:28
@Torsten
A B C D
164 -6
269 3
2 5 10 -3
3610 No flipped row (6,3) so preserve C value (=10)
4345 No flipped row (3,4), preserve C value (=45)
5 2 13 3
626 -3
6110 6
Image Analyst il 23 Giu 2024 alle 14:49
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Apri in MATLAB Online
Do you have a table variable, or a double variable? Can you attach your variable in a mat file?
save('answers.mat', 'T');
When you say "flipped" do you mean vertically or horizontally? Your original example seemed to have it both ways. Now it seems just that you mean horizontally, so that columnA is in columnB and ColumnB is in columnA, so in essence for a particular row, colA and colB are swapped.
If you have any more questions, then attach your data and code to read it in with the paperclip icon after you read this:
TUTORIAL: How to ask a question (on Answers) and get a fast answer
Neel Kulkarni il 23 Giu 2024 alle 15:20
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- answers.mat
@Image Analyst Hi, it is a table variable. I have attached the mat file with my example above. It indeed is a horizontal flip.
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Risposte (1)
dpb il 23 Giu 2024 alle 16:35
Modificato: dpb il 24 Giu 2024 alle 15:56
Apri in MATLAB Online
- answers.mat
load answers T
T
T = 8x3 table
A B C _ _ __ 1 6 4 2 6 9 2 5 10 3 6 10 4 3 45 5 2 13 6 2 6 6 1 10
T.D=nan(height(T),1);
for i=1:height(T)
ix=find(all(fliplr(T{:,1:2})==T{i,1:2},2));
try
T.D(i)=T.C(i)-T.C(ix);
catch
end
end
T
T = 8x4 table
A B C D _ _ __ ___ 1 6 4 -6 2 6 9 3 2 5 10 -3 3 6 10 NaN 4 3 45 NaN 5 2 13 3 6 2 6 -3 6 1 10 6
The above is the "dead ahead" solution that computes the difference for every record in the file; one could be a little more clever and set both i and ix (to the negative difference) in the one loop iteration. Then one would need to make and update the list of records yet to be handled to know when to quit. The list would start initialized to 1:height(T) and each i, ix would be removed each iteration. When empty, quit.
The above does nothing when there is no match, thereby leaving the initial default NaN value; your choice as to what to do here if this isn't the desired result. Your initial example had no unpaired records and your followup didn't define what is the desired result for those records. In this case, the catch clause would have to remove those i entries. Whether shortening the number of iterations would "win" over the extra logic probably would depend upon how large T is.
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