Use variable to find column in table

I am trying to reset a tables values to 0.

The sceanario may change every time. So I am using table.Properties.VariableNames to find the names of the columns and then I was trying to cycle through the columns using the names stores in table.Properties.VariableNames so I could assign the reset values.

For example, I have a table with 5 columns called A to E

var=table.Properties.VariableNames

var={'A','B','C','D','E'}

table.var(1)=zeros(size(table.var(1)))

The error is that var is not a table column name which is true, but what is stored inside var is. I have to do it like this as one of the columns is actually a mini table and using size(table(:,10)) gives 12 1 but its actually 12 4. using size(table.var10) gives the correct answertab

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

You can either use T{:,X} or T.(X) to access any variable using expression X.

Answer 1

[Voss]

% a table with 5 columns, one of which is a table with 4 columns:
t = table(rand(12,1),rand(12,1), ...
    array2table(rand(12,4),'VariableNames',"C"+(1:4)), ...
    rand(12,1),rand(12,1), ...
    'VariableNames',{'A','B','C','D','E'});
var = t.Properties.VariableNames;

disp(t)

       A           B                             C                            D          E    
                               C1          C2         C3          C4                          
    ________    ________    ___________________________________________    _______    ________

     0.72865     0.95941     0.87349     0.26227    0.42639     0.96083    0.14744     0.77161
     0.85309     0.62403     0.19329     0.28628       0.33      0.6298    0.99507     0.60549
     0.73144     0.60098     0.95765     0.69378    0.15803     0.28751    0.31233     0.38058
     0.53602     0.59152     0.68489     0.52386    0.18541     0.37659    0.59207     0.49533
     0.30399     0.29887      0.8184     0.63234    0.62179     0.76149    0.34043      0.6088
    0.011554     0.39662     0.58962    0.064497    0.34494       0.795    0.48311     0.50604
     0.66965     0.45485     0.51885     0.47429    0.86962     0.27364    0.80457       0.183
     0.34735     0.83887     0.73486      0.1568    0.91418     0.82387    0.66479      0.9985
     0.70295    0.027005     0.41849    0.036909    0.61908     0.58419    0.89819     0.27984
     0.13258     0.58911     0.86353     0.78146    0.28787     0.16293    0.73759     0.52051
      0.4701    0.024021    0.077109     0.80098    0.70586    0.069148    0.78371     0.62528
     0.54768     0.15003     0.67575     0.31717    0.29992     0.63877    0.78844    0.041964

Use this syntax to refer to a table column's contents when the column names are stored in var:

t.(var{1})

ans = 12×1

0.7287 0.8531 0.7314 0.5360 0.3040 0.0116 0.6697 0.3474 0.7029 0.1326

t.(var{3})

ans = 12×4 table
       C1          C2         C3          C4   
    ________    ________    _______    ________

     0.87349     0.26227    0.42639     0.96083
     0.19329     0.28628       0.33      0.6298
     0.95765     0.69378    0.15803     0.28751
     0.68489     0.52386    0.18541     0.37659
      0.8184     0.63234    0.62179     0.76149
     0.58962    0.064497    0.34494       0.795
     0.51885     0.47429    0.86962     0.27364
     0.73486      0.1568    0.91418     0.82387
     0.41849    0.036909    0.61908     0.58419
     0.86353     0.78146    0.28787     0.16293
    0.077109     0.80098    0.70586    0.069148
     0.67575     0.31717    0.29992     0.63877

Using that, here is one way to set everything to 0:

for ii = 1:numel(var)
    if istable(t.(var{ii}))
        t.(var{ii}){:,:} = 0;
    else
        t.(var{ii})(:) = 0;
    end
end

disp(t)

    A    B             C              D    E
              C1    C2    C3    C4          
    _    _    ____________________    _    _

    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0
    0    0    0     0     0     0     0    0

[Katherine]

This works great and helped made my code more efficient. Your answer was so easy to understand, thank you

[Voss]

You're welcome!

Answer 2

[Mathieu NOE]

hello

maybe this ? here we want to reset the B column

m = 10,

m = 10

n = 3;
t = array2table(rand(m,n),'VariableNames',{'A' 'B' 'C'})

t = 10×3 table
       A          B           C    
    _______    _______    _________

    0.32001    0.97943      0.51794
    0.39286    0.79694      0.68753
    0.61581    0.71661      0.85918
     0.7122    0.33171       0.6402
    0.89579    0.68001      0.43428
    0.93457    0.24604     0.096676
    0.69047    0.23767       0.5885
    0.14564    0.79213      0.58002
    0.68773    0.32087    0.0058992
    0.46555    0.92998      0.89511

var=t.Properties.VariableNames;

col2reset_name = "B";
index = find(contains(var,col2reset_name));
t(:,2) = array2table(zeros(m,1))

t = 10×3 table
       A       B        C    
    _______    _    _________

    0.32001    0      0.51794
    0.39286    0      0.68753
    0.61581    0      0.85918
     0.7122    0       0.6402
    0.89579    0      0.43428
    0.93457    0     0.096676
    0.69047    0       0.5885
    0.14564    0      0.58002
    0.68773    0    0.0058992
    0.46555    0      0.89511

Answer 3

[Steven Lord]

Note that as shown on the documentation page linked to by @Stephen23, you can access data in a table using variable names, logical arrays, or subscripts.

A = array2table(magic(4))

A = 4×4 table
    Var1    Var2    Var3    Var4
    ____    ____    ____    ____

     16       2       3      13 
      5      11      10       8 
      9       7       6      12 
      4      14      15       1 

B1 = A.Var3

B1 = 4×1

3 10 6 15

B2 = A{:, "Var3"}

B2 = 4×1

3 10 6 15

B3 = A{:, 3}

B3 = 4×1

3 10 6 15

B4 = A{:, [false false true false]}

B4 = 4×1

3 10 6 15

Converting a subset of a list of variable names in a table to either subscripts (as B3) or a logical mask (as B4) is pretty easy.

varnames = ["Var2", "Var4"]

varnames = 1×2 string array
    "Var2"    "Var4"

mask = ismember(A.Properties.VariableNames, varnames)

mask = 1×4 logical array
   0   1   0   1

subscripts = find(mask)

subscripts = 1×2

2 4