Mesh grid from 3-column table

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Morten Nissov
Morten Nissov on 8 Apr 2021
Edited: Cris LaPierre on 8 Apr 2021
I have a table with values extracted from a csv I want to transform into a grid.
Let's use this table as an example
tdata.x = [1;2;1;2];
tdata.y = [3;3;4;4];
tdata.z = randn(4,1);
tdata=struct2table(tdata);
>> tdata
tdata =
4×3 table
x y z
_ _ _______
1 3 0.53767
2 3 1.8339
1 4 -2.2588
2 4 0.86217
I would like to pivot this into a 2x2 z matrix where rows/columns are given by y and x respectively, something in this direction:
x 1 2
y
3 0.53767 1.8339
4 -2.2588 0.86217
where the first row are the x coordinates, the first columns is the y coordinates and in-between are the corresponding z-values. So that is to say the z-value corresponding to (x,y)=(1,4) is -2.2588.
Note, I am going to use this grid for other things down the road so solutions involving interpolation are not valid, as well the data is guaranteed to be given on a grid.

Answers (1)

Cris LaPierre
Cris LaPierre on 8 Apr 2021
Edited: Cris LaPierre on 8 Apr 2021
I think you could achieve something like that using sortrows and reshape.
x = [1;2;1;2];
y = [3;3;4;4];
z = randn(4,1);
tdata=table(x,y,z);
tdata = sortrows(tdata,["x","y"])
tdata = 4×3 table
x y z _ _ ________ 1 3 0.28228 1 4 -0.50085 2 3 1.437 2 4 -0.26357
tmat = array2table(reshape(tdata.z,length(unique(tdata.x)),length(unique(tdata.y))),...
'RowNames',string(unique(tdata.y)),'VariableNames',string(unique(tdata.x)))
tmat = 2×2 table
1 2 ________ ________ 3 0.28228 1.437 4 -0.50085 -0.26357
Now use can use the variable names and row names to access your data from the table. The syntax you elect to use to access the data will determine your input order.
% (rows,variable)
Zval = tmat{"4","1"}
Zval = -0.5008
% Alternate syntax
Zval = tmat.("1")("4")
Zval = -0.5008

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