Making a table from data using rec

I am trying to use this code to create a table of when the data is in recession (when the value of q(x)>q(x-1)). However I do not know how to use the rec command.

T= readtable ("GDF.xlsx");
q=T(:,2);%The second column of the data is numerical, the first column is just dates
R=0;
for x=T
    if q(x)>q(x-1) %Defining what a recession counts as
        R=R+1;
        rec(x)=1 %If it is a recession it =1, if not it will =0
    else
        rec(x)=0;
    end
end

Error message that appears when I run this code:

Error using () (line 133)

Subscripting into a table using one subscript (as in t(i))

is not supported. Specify a row subscript and a variable

subscript, as in t(rows,vars). To select variables, use

t(:,i) or for one variable t.(i). To select rows, use

t(i,:).

Error in

Week4Q2 (line 8)

if q(x)>q(x-1)

Any idea on how to change the code so it produces a table of when the data is in recession? Help would be appreciated.

Answer 1

[Star Strider]

Apparently, 'rec' is not a funciton. Here it is simply a vector.

I am not certain what 'R' is doing other than keeping a count. You can do that easily enough with the nnz funciton after the loop completes.

What sort of table do you want your code to produce? The 'rec' vector is a logical vector, so you can use it to produce a table of values where only 'rec' is true or conversely when it is false.

T= readtable ("GDF.xlsx")

T = 16708×2 table
       Var1        Var2 
    ___________    _____

    03-Jan-1979    0.026
    04-Jan-1979    0.021
    05-Jan-1979    0.019
    06-Jan-1979    0.019
    07-Jan-1979    0.519
    08-Jan-1979    0.214
    09-Jan-1979    0.371
    10-Jan-1979    0.483
    11-Jan-1979    0.145
    12-Jan-1979     0.06
    13-Jan-1979    0.025
    14-Jan-1979    0.027
    15-Jan-1979    0.029
    16-Jan-1979    0.069
    17-Jan-1979    0.263
    18-Jan-1979    0.108

rec = false(size(T.Var1));              % Preallocate

q=T{:,2};%The second column of the data is numerical, the first column is just dates
R=0;
for x=2:numel(rec)
    if q(x)>q(x-1) %Defining what a recession counts as
        R=R+1;
        rec(x)=1; %If it is a recession it =1, if not it will =0
    else
        rec(x)=0;
    end
end
R

R = 5377

rec_true = nnz(rec)

rec_true = 5377

rec_true_table = T(rec,:)                       % Table Of 'true' 'rec' Values

rec_true_table = 5377×2 table
       Var1        Var2 
    ___________    _____

    07-Jan-1979    0.519
    09-Jan-1979    0.371
    10-Jan-1979    0.483
    14-Jan-1979    0.027
    15-Jan-1979    0.029
    16-Jan-1979    0.069
    17-Jan-1979    0.263
    19-Jan-1979    0.356
    20-Jan-1979    0.469
    24-Jan-1979    0.092
    25-Jan-1979     1.05
    28-Jan-1979     0.25
    29-Jan-1979    0.633
    31-Jan-1979    0.191
    01-Feb-1979     1.69
    06-Feb-1979    0.323

rec_false_table = T(~rec,:)                     % Table Of 'false' 'rec' Values

rec_false_table = 11331×2 table
       Var1        Var2 
    ___________    _____

    03-Jan-1979    0.026
    04-Jan-1979    0.021
    05-Jan-1979    0.019
    06-Jan-1979    0.019
    08-Jan-1979    0.214
    11-Jan-1979    0.145
    12-Jan-1979     0.06
    13-Jan-1979    0.025
    18-Jan-1979    0.108
    21-Jan-1979    0.151
    22-Jan-1979    0.085
    23-Jan-1979    0.059
    26-Jan-1979    0.248
    27-Jan-1979    0.101
    30-Jan-1979    0.179
    02-Feb-1979    0.287

EDIT -- (22 Oct 2025 at 15:30)

Added 'rec_true_table' and 'rec_false_table'.

.

Answer 2

[Mathieu NOE]

hello

here you are

what has changed

• q must be converted from table to array - use table2array
• for loop index needed a fix : now it's : for x=2:numel(q) - this also implies that we must declare the first value of rec ( by default) is either 0 or 1 - there is no previous q value to test the recession

the updated code result with your supplied excel file gives R = 5377 recessions

T= readtable ("GDF.xlsx");
q=table2array(T(:,2));%The second column of the data is numerical, the first column is just dates
R=0;
rec(1) = 0;
for x=2:numel(q)
    if q(x)>q(x-1) %Defining what a recession counts as
        R=R+1;
        rec(x)=1; %If it is a recession it =1, if not it will =0
    else
        rec(x)=0;
    end
end

[Stephen23]

"q must be converted from table to array - use table2array"

It is simpler to use the correct indexing:

q = T{:,2};

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

[Mathieu NOE]

yes , of course !!

[Mathieu NOE]

@Nathan

you can also use diff function to check the recession - instead of the for loop

see second alternative hereafter which is 10 times faster and more concise

T= readtable ("GDF.xlsx");
q=T{:,2};%The second column of the data is numerical, the first column is just dates

% your method
tic
R=0;
rec(1) = 0;
for x=2:numel(q)
    if q(x)>q(x-1) %Defining what a recession counts as
        R=R+1;
        rec(x)=1; %If it is a recession it =1, if not it will =0
    else
        rec(x)=0;
    end
end

toc

Elapsed time is 0.027264 seconds.

% another method
tic

rec2 = diff(q)>0; % logical array 
% rec2 will be identical to rec but with one sample shift du to diff
% operation
% here we add a logical 0 (false) at the start (which is equivalent to the
% initilaization rec(1) = 0 as we did above in the first method);
rec2 = [false;rec2]; % add a logical 0 (false) at the start

toc

Elapsed time is 0.002681 seconds.

% let's compare the first 20 values side by side 
n = 20;
sidebyside = [rec(1:n)' rec2(1:n)]

sidebyside = 20×2

0 0 0 0 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 1 1

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% create you output table 
true_table = T(rec2,:)  

true_table = 5377×2 table
       Var1        Var2 
    ___________    _____

    07-Jan-1979    0.519
    09-Jan-1979    0.371
    10-Jan-1979    0.483
    14-Jan-1979    0.027
    15-Jan-1979    0.029
    16-Jan-1979    0.069
    17-Jan-1979    0.263
    19-Jan-1979    0.356
    20-Jan-1979    0.469
    24-Jan-1979    0.092
    25-Jan-1979     1.05
    28-Jan-1979     0.25
    29-Jan-1979    0.633
    31-Jan-1979    0.191
    01-Feb-1979     1.69
    06-Feb-1979    0.323

Answer 3

[Voss]

T = readtable("GDF.xlsx");
q = T.(2); % second column of the data

% logical index of "rec" rows, according
% to the definition of "rec":
idx_rec = [false; q(2:end) > q(1:end-1)]; 

% table of only the "rec" rows from T:
T_rec = T(idx_rec,:);