Using multiple functions on a variable in a table

I have a table (T) of data 365x3. With column variables A,B,C lets say. I am trying to create a new column (D) where 2 functions would be necessary for the new variable. I run into an error that the size of the left and right do not match. I have tried 3 different approaches with no success, shown below. I am not too sure how to fix this?

%Method 1
T.D = 1000 * (2834.1 - 0.29 * T.B - 0.004 * T.B.^(2.0));
idx = T.B >= 0;
T.D(idx) = 1000 * (2501 - 2.36 * T.B);

%Method 2
idx = T.B < 0;
T.D(idx) = 1000 * (2834.1 - 0.29 * T.B - 0.004 * T.B.^(2.0));
idx2 = T.B >= 0;
T.D(idx2) = 1000 * (2501 - 2.36 * T.B);

%Method 3
idx = T{:,'B'} < 0;
T{idx,'D'} = 1000 * (2834.1 - 0.29 * T{:,'B'} - 0.004 * T{:,'B'}.^(2.0));
idx2 = T{:,'B'} >= 0;
T{idx2,'D'} = 1000 * (2501 - 2.36 * T{:,'B'});

Answer 1

[Stef1998]

A bit tedious and Im sure there might be a faster method out there but this solves the problem

T.D1 = 1000 * (2834.1 - 0.29 * T.B - 0.004 * T.B.^(2.0));
T.D1(T.B>=0) = 0;

T.D2 = 1000 * (2501 - 2.36 * T.B);
T.D2(T.B<0) = 0;

T.D = T.D1 + T.D2;

Answer 2

[Dave B]

How about just initializing the new table variable first (e.g. with NaN values) and then populating it using your indices?

T = table(rand(100,1));
T.Var2 = nan(height(T), 1);
T.Var2(T.Var1<.5) = -1;
T.Var2(T.Var1>=.5) = 1

T = 100×2 table
      Var1      Var2
    ________    ____

     0.59525      1 
     0.89591      1 
      0.3016     -1 
     0.94513      1 
     0.38489     -1 
      0.3707     -1 
     0.20688     -1 
    0.066268     -1 
     0.07012     -1 
     0.97702      1 
     0.23667     -1 
     0.97863      1 
     0.56713      1 
      0.9572      1 
     0.93443      1 
      0.5219      1 

[Stef1998]

That would be similar to what i did for method one but because I use an equation that references another variable it still does not work since the left and right sides have different elements. It would read more like

T = table(rand(100,1));
T.Var2 = nan(height(T), 1);
T.Var2(T.Var1<.5) = 3.2*T.Var1;

Unable to perform assignment because the left and right sides have a different number of elements.

T.Var2(T.Var1>=.5) = 4.2*T.Var1;

[Dave B]

Your snippet was just missing the index in the right hand side

T = table(rand(100,1));
T.Var2 = nan(height(T), 1);
ind = T.Var1<.5;
T.Var2(ind) = 3.2*T.Var1(ind);
T.Var2(~ind) = 4.2*T.Var1(~ind)

T = 100×2 table
      Var1        Var2  
    ________    ________

     0.61477       2.582
    0.022891    0.073253
     0.51972      2.1828
     0.40734      1.3035
     0.10431      0.3338
     0.50238        2.11
     0.69675      2.9263
     0.82957      3.4842
     0.41558      1.3298
     0.12382     0.39623
     0.50392      2.1164
      0.9992      4.1967
     0.61337      2.5762
     0.69751      2.9295
     0.96018      4.0328
     0.82302      3.4567