Use table row as input for a new table

Question

Metin Akyol 2022-6-16

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回答： Steven Lord 2022-6-16

I would like to create a new table that has 2 columns. These columns are supposed to be filled with the values from the rows of 2 other tables. So basically:

target_table:

col1 col2

x1 y1

x2 y2

x3 y3

table1:

col1 col2 col3

x1 x2 x3

table2:

col1 col2 col3

y1 y2 y3

I was thinking something simple like this but I keep on getting errors of size mismatches or I ned up wit hthe values from the table becoming strings or cells:

target_table(:,"col1") = rows2vars(tail(table1,1))

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Answer 1

Kevin Holly 2022-6-16

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Are you starting off with vector arrays or tables? Note, below would also work if you used numeric values instead of strings.

See below if you start off with tables:

table1 = table;
table1.col1 = "x1";
table1.col2 = "x2";
table1.col3 = "x3"
table1 = 1×3 table
    col1    col2    col3
    ____    ____    ____

    "x1"    "x2"    "x3"
table2 = table;
table2.col1 = "y1";
table2.col2 = "y2";
table2.col3 = "y3"
table2 = 1×3 table
    col1    col2    col3
    ____    ____    ____

    "y1"    "y2"    "y3"
target_table=table;
target_table.col1 = table2array(table1(:,:))';
target_table.col2 = table2array(table2(:,:))'
target_table = 3×2 table
    col1    col2
    ____    ____

    "x1"    "y1"
    "x2"    "y2"
    "x3"    "y3"

See below if you start off with vector arrays:

table1 = table2array(table1)
table1 = 1×3 string array
    "x1"    "x2"    "x3"
table2 = table2array(table2)
table2 = 1×3 string array
    "y1"    "y2"    "y3"
target_table=table;
target_table.col1 = table1';
target_table.col2 = table2'
target_table = 3×2 table
    col1    col2
    ____    ____

    "x1"    "y1"
    "x2"    "y2"
    "x3"    "y3"

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Metin Akyol 2022-6-16

Perfect, thank you!! Exactly what I was looking for.

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Answer 2

Steven Lord 2022-6-16

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Let's make two sample tables.

T1 = array2table(1:3);
T2 = array2table(4:6);

Create a third table to hold the data from the first two. The "magic number" 2 in the line below comes from the fact that I know I'm combining two tables. If you're in a situation where you need that number to be dynamic and/or much larger than 2 that's a sign that you may want to rethink your approach and revise your code to avoid creating T1, T2, T3, T4, ...

T = table('size', [width(T1), 2], 'VariableTypes', {'double', 'double'})
T = 3×2 table
    Var1    Var2
    ____    ____

     0       0  
     0       0  
     0       0  

Now assuming all the variables in T1 can be concatenated (with conversion, if necessary) you can use T1.Variables to extract all the data as an array. This array can be transposed and put into one of the variables in T. The same holds for T2.

T{:, 1} = (T1.Variables).';
T{:, 2} = (T2.Variables).'
T = 3×2 table
    Var1    Var2
    ____    ____

     1       4  
     2       5  
     3       6  