How to write a loop for this purpose?

Hey all,

I have a 34*1 cell (let's call it precips). I would like to have a loop in order to do this:

1982 = precips {1, 1};

1983= precips {2, 1};

1984= precips {3, 1};

1985= precips {4, 1};

.

.

.

2015= precips {34, 1};

what is the code for the loop?

[Daniel M]

I recommend not trying to do this, for dozens of reasons. <https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval>

[BN]

I read the article that you attached. I just want to know how to write a loop in this condition. do you have any alternative way?

if it possible I want to know what is the loop in this case.

thank you :)

[Daniel M]

I refuse to encourage this type of coding. (And those are invalid names for variables anyways).

[BN]

ok I understand you.

so you mean that I should type every 34 years by my hand instead of using loop, right?

Answer 1

[Walter Roberson]

for iter = 1 : size(precips,1)
    year = 1981 + iter;
    cmd = sprintf('%d = precips{%d,1}', year, iter);
    eval(cmd);
end

[Walter Roberson]

filename = 'This_Is_A_Bad_Idea.m';
fid = fopen(filename, 'w');
for iter = 1 : size(precips,1);
    year = 1981 + iter;
    fprintf(fid, '%d = precips{%d,1};', year, iter);
end
fclose(fid);

After which you can

run(filename)

[BN]

Thank you, Walter, for letting me know that this is a bad idea. I saw some alternative ways in

<https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval>

but the content of my precips cell is 3d arrays, like:

precips{1, 1}= 720*360*365 (see the screenshot attached)

I just want to export these 3d arrays inside precips to my workplace, in order to use in the rest of calculation code. do you know any other better way?

actually:

for iter = 1 : size(precips,1)
    year = 1981 + iter;
    cmd = sprintf('%d = precips{%d,1}', year, iter);
    eval(cmd);
end

gaves me following error:

Error: Incorrect use of '=' operator. To assign a value to a variable,
use '='. To compare values for equality, use '=='. 

I want to do all these things in order to convert 34 NetCDF files that are in a daily basis (from 1982 to 2015) to monthly some for each year and then use them to build one comprehensive 3d array for all period of 1982-2015.

many thanks

[Walter Roberson]

There error is to be expected.

1982 = precips {1, 1};

is not a permitted syntax. But you didn't care about that earlier: you just wanted to know how to write the code to do it anyhow, so I wrote the code to do it anyhow.

I just want to export these 3d arrays inside precips to my workplace, in order to use in the rest of calculation code.

They already are inside your workspace.

num_years = size(precips,1);
all_sums = zeros(720, 360, num_years, 12);
for iter = 1 : num_years
    thisdata = permute(precips{iter,1}, [3 1 2]);
    year = 1981 + iter;
    ts = datetime([year, 1, 0]) + days(1:size(thisdata,1)).'; %column vector
    G = month(ts);
    month_sum = permute(splitapply(@sum, thisdata, G), [2 3 4 1]);
    all_sums(:,:,iter,:) = month_sum;
end

all_sums should now be a 720 x 360 x 34 x 12 array, where the 4th dimension is the month number.

It is not immediately obvious how you want to order the per-month data for all years into a 3D array.