How can i change file within a loop?

 %two snippets of code
---------------------------------------------------------------- 
 gauge.source='PSMSL';
 gauge.data(1).location='Vlissingen';               gauge.data(1).id='20';
 gauge.data(2).location='Hoek van Holland';            gauge.data(2).id='22';
 gauge.data(3).location='Roompot Buiten';          gauge.data(3).id='470';
 gauge.data(4).location='Zeebrugge';             gauge.data(4).id='1551';
-----------------------------------------------------
%snippet 2 
---------------------------------------------------------
filename = 'psmsl_monthly_20.txt';

% Open the file and read all lines to determine the number of lines
fileID = fopen(filename, 'r');
v = textscan(fileID, '%s%*[^\n]');
fclose(fileID);

------------------------------------------------------

So far everything runs But i want to change the filename voor more datat to read Ihav tried with numstring but I cannor figure out what I do wrong. Now my code runs but de data from Vlissingen are used for the other stations to. (ID 20)

How can i replace the code

filename = 'psmsl_monthly_20.txt';

to something like filename = 'psmsl_monthly_ "next station id".txt'; and let thecode read all the files.

Ellen

Answer 1

[Jon]

I think you are looking for something like this

for k = 1:12
    filename = ['psmsl_monthly_',num2str(k),'.txt']
    % do something with filename, etc.
end

filename = 'psmsl_monthly_1.txt'

filename = 'psmsl_monthly_2.txt'

filename = 'psmsl_monthly_3.txt'

filename = 'psmsl_monthly_4.txt'

filename = 'psmsl_monthly_5.txt'

filename = 'psmsl_monthly_6.txt'

filename = 'psmsl_monthly_7.txt'

filename = 'psmsl_monthly_8.txt'

filename = 'psmsl_monthly_9.txt'

filename = 'psmsl_monthly_10.txt'

filename = 'psmsl_monthly_11.txt'

filename = 'psmsl_monthly_12.txt'

[Jon]

Or if you have leading zeros, for example, psmsl_monthly_08.txt, you can use

for k = 1:12
    filename = ['psmsl_monthly_',num2str(k,'%02.f'),'.txt']
    % do something with filename, etc.
end

filename = 'psmsl_monthly_01.txt'

filename = 'psmsl_monthly_02.txt'

filename = 'psmsl_monthly_03.txt'

filename = 'psmsl_monthly_04.txt'

filename = 'psmsl_monthly_05.txt'

filename = 'psmsl_monthly_06.txt'

filename = 'psmsl_monthly_07.txt'

filename = 'psmsl_monthly_08.txt'

filename = 'psmsl_monthly_09.txt'

filename = 'psmsl_monthly_10.txt'

filename = 'psmsl_monthly_11.txt'

filename = 'psmsl_monthly_12.txt'

[Ellen]

Ive already defined de 4 stations with the number

gauge.source='PSMSL';

gauge.data(1).location='Vlissingen'; gauge.data(1).id='20';

gauge.data(2).location='Hoek van Holland'; gauge.data(2).id='22';

gauge.data(3).location='Roompot Buiten'; gauge.data(3).id='470';

gauge.data(4).location='Zeebrugge'; gauge.data(4).id='1551';

should I use 1,2,3 and 4 for k (k = station)

for stat=1:4

filename = ['psmsl_monthly_', num2str(gauge.data(stat).id), '.txt'];

it seems to work

Ellen

[Jon]

Yes it makes sense that if you have defined an array of station id's in your case, 20, 22, 470, 1551 corresponding to different locations, then you can index through those in your loop, e.g. stat = 1:4, obtain the corresponding station id, e.g. guage.data(stat).id, and then convert that to a string to get the corresponding file name for that station.

By the way, If this was just a follow up question on my answer, you could put it in as a comment rather than a new answer. Otherwise it's also ok to post your own solution as an alternative answer, but maybe not so easy for someone to follow the flow of the thread if that wasn't what you intended.

[Voss]

@Ellen:

gauge.source='PSMSL';
gauge.data(1).location='Vlissingen';       gauge.data(1).id='20';
gauge.data(2).location='Hoek van Holland'; gauge.data(2).id='22';
gauge.data(3).location='Roompot Buiten';   gauge.data(3).id='470';
gauge.data(4).location='Zeebrugge';        gauge.data(4).id='1551';

There is no need for num2str in this case because the ids are already character vectors:

for stat = 1:numel(gauge.data)
    filename = ['psmsl_monthly_', gauge.data(stat).id, '.txt'];
    disp(filename);
end

psmsl_monthly_20.txt
psmsl_monthly_22.txt
psmsl_monthly_470.txt
psmsl_monthly_1551.txt

You could also construct all the file names at once before the loop:

filenames = strcat('psmsl_monthly_',{gauge.data.id},'.txt');
for stat = 1:numel(gauge.data)
    filename = filenames{stat};
    disp(filename);
end

psmsl_monthly_20.txt
psmsl_monthly_22.txt
psmsl_monthly_470.txt
psmsl_monthly_1551.txt

[Jon]

Hi @Voss, good catch that in the OP's example the ID numbers were already strings and wouldn't need to be converted. I hadn't noticed that and just assumed they would be numerical values.

I'm not sure if this was really what was intended though, or whether that would be a good idea. In general it seems better to me to keep numerical values as numbers and not strings unless there is a really good reason not to.

[Ellen]

You helped a lot already but now I get NaN in de matrix

Il attach the code I am working with (and where i may have put some wrong brackets or so)

the psmsl_kopie.mat is what i try tot get from my code using different stations and a much newer mathlab version

I cannot include dat files so here te txt file from the student.--dat which is used for the statistics.

underneath a small part of a psmsl_monthly wile with 3 years of data. there are only diffrences in the second colums of the for files

this is what I get.

this is what the mat file should look like

but not NaN in the 1x27 double

 0        0.10    0.05   0.025   0.1     0.005   0.001
  1.0      3.078   6.314  12.706  31.821  63.657 318.313
  2.0      1.886   2.920   4.303   6.965   9.925  22.327
  3.0      1.638   2.353   3.182   4.541   5.841  10.215
  4.0      1.533   2.132   2.776   3.747   4.604   7.173
  5.0      1.476   2.015   2.571   3.365   4.032   5.893
  6.0      1.440   1.943   2.447   3.143   3.707   5.208
  7.0      1.415   1.895   2.365   2.998   3.499   4.782
  8.0      1.397   1.860   2.306   2.896   3.355   4.499
  9.0      1.383   1.833   2.262   2.821   3.250   4.296
 10.0      1.372   1.812   2.228   2.764   3.169   4.143
 11.0      1.363   1.796   2.201   2.718   3.106   4.024
 12.0      1.356   1.782   2.179   2.681   3.055   3.929
 13.0      1.350   1.771   2.160   2.650   3.012   3.852
 14.0      1.345   1.761   2.145   2.624   2.977   3.787
 15.0      1.341   1.753   2.131   2.602   2.947   3.733
 16.0      1.337   1.746   2.120   2.583   2.921   3.686
 17.0      1.333   1.740   2.110   2.567   2.898   3.646
 18.0      1.330   1.734   2.101   2.552   2.878   3.610
 19.0      1.328   1.729   2.093   2.539   2.861   3.579
 20.0      1.325   1.725   2.086   2.528   2.845   3.552
 21.0      1.323   1.721   2.080   2.518   2.831   3.527
 22.0      1.321   1.717   2.074   2.508   2.819   3.505
 23.0      1.319   1.714   2.069   2.500   2.807   3.485
 24.0      1.318   1.711   2.064   2.492   2.797   3.467
 25.0      1.316   1.708   2.060   2.485   2.787   3.450
 26.0      1.315   1.706   2.056   2.479   2.779   3.435
 27.0      1.314   1.703   2.052   2.473   2.771   3.421
 28.0      1.313   1.701   2.048   2.467   2.763   3.408
 29.0      1.311   1.699   2.045   2.462   2.756   3.396
 30.0      1.310   1.697   2.042   2.457   2.750   3.385
 31.0      1.309   1.696   2.040   2.453   2.744   3.375
 32.0      1.309   1.694   2.037   2.449   2.738   3.365
 33.0      1.308   1.692   2.035   2.445   2.733   3.356
 34.0      1.307   1.691   2.032   2.441   2.728   3.348
 35.0      1.306   1.690   2.030   2.438   2.724   3.340
 36.0      1.306   1.688   2.028   2.434   2.719   3.333
 37.0      1.305   1.687   2.026   2.431   2.715   3.326
 38.0      1.304   1.686   2.024   2.429   2.712   3.319
 39.0      1.304   1.685   2.023   2.426   2.708   3.313
 40.0      1.303   1.684   2.021   2.423   2.704   3.307
 41.0      1.303   1.683   2.020   2.421   2.701   3.301
 42.0      1.302   1.682   2.018   2.418   2.698   3.296
 43.0      1.302   1.681   2.017   2.416   2.695   3.291
 44.0      1.301   1.680   2.015   2.414   2.692   3.286
 45.0      1.301   1.679   2.014   2.412   2.690   3.281
 46.0      1.300   1.679   2.013   2.410   2.687   3.277
 47.0      1.300   1.678   2.012   2.408   2.685   3.273
 48.0      1.299   1.677   2.011   2.407   2.682   3.269
 49.0      1.299   1.677   2.010   2.405   2.680   3.265
 50.0      1.299   1.676   2.009   2.403   2.678   3.261
 51.0      1.298   1.675   2.008   2.402   2.676   3.258
 52.0      1.298   1.675   2.007   2.400   2.674   3.255
 53.0      1.298   1.674   2.006   2.399   2.672   3.251
 54.0      1.297   1.674   2.005   2.397   2.670   3.248
 55.0      1.297   1.673   2.004   2.396   2.668   3.245
 56.0      1.297   1.673   2.003   2.395   2.667   3.242
 57.0      1.297   1.672   2.002   2.394   2.665   3.239
 58.0      1.296   1.672   2.002   2.392   2.663   3.237
 59.0      1.296   1.671   2.001   2.391   2.662   3.234
 60.0      1.296   1.671   2.000   2.390   2.660   3.232
 61.0      1.296   1.670   2.000   2.389   2.659   3.229
 62.0      1.295   1.670   1.999   2.388   2.657   3.227
 63.0      1.295   1.669   1.998   2.387   2.656   3.225
 64.0      1.295   1.669   1.998   2.386   2.655   3.223
 65.0      1.295   1.669   1.997   2.385   2.654   3.220
 66.0      1.295   1.668   1.997   2.384   2.652   3.218
 67.0      1.294   1.668   1.996   2.383   2.651   3.216
 68.0      1.294   1.668   1.995   2.382   2.650   3.214
 69.0      1.294   1.667   1.995   2.382   2.649   3.213
 70.0      1.294   1.667   1.994   2.381   2.648   3.211
 71.0      1.294   1.667   1.994   2.380   2.647   3.209
 72.0      1.293   1.666   1.993   2.379   2.646   3.207
 73.0      1.293   1.666   1.993   2.379   2.645   3.206
 74.0      1.293   1.666   1.993   2.378   2.644   3.204
 75.0      1.293   1.665   1.992   2.377   2.643   3.202
 76.0      1.293   1.665   1.992   2.376   2.642   3.201
 77.0      1.293   1.665   1.991   2.376   2.641   3.199
 78.0      1.292   1.665   1.991   2.375   2.640   3.198
 79.0      1.292   1.664   1.990   2.374   2.640   3.197
 80.0      1.292   1.664   1.990   2.374   2.639   3.195
 81.0      1.292   1.664   1.990   2.373   2.638   3.194
 82.0      1.292   1.664   1.989   2.373   2.637   3.193
 83.0      1.292   1.663   1.989   2.372   2.636   3.191
 84.0      1.292   1.663   1.989   2.372   2.636   3.190
 85.0      1.292   1.663   1.988   2.371   2.635   3.189
 86.0      1.291   1.663   1.988   2.370   2.634   3.188
 87.0      1.291   1.663   1.988   2.370   2.634   3.187
 88.0      1.291   1.662   1.987   2.369   2.633   3.185
 89.0      1.291   1.662   1.987   2.369   2.632   3.184
 90.0      1.291   1.662   1.987   2.368   2.632   3.183
 91.0      1.291   1.662   1.986   2.368   2.631   3.182
 92.0      1.291   1.662   1.986   2.368   2.630   3.181
 93.0      1.291   1.661   1.986   2.367   2.630   3.180
 94.0      1.291   1.661   1.986   2.367   2.629   3.179
 95.0      1.291   1.661   1.985   2.366   2.629   3.178
 96.0      1.290   1.661   1.985   2.366   2.628   3.177
 97.0      1.290   1.661   1.985   2.365   2.627   3.176
 98.0      1.290   1.661   1.984   2.365   2.627   3.175
 99.0      1.290   1.660   1.984   2.365   2.626   3.175
100.0      1.290   1.660   1.984   2.364   2.626   3.174


the first three year of station 20 
1996.0417   6699  0 000
1996.1250   6765  0 000
1996.2083   6677  0 000
1996.2917   6753  0 000
1996.3750   6837  0 000
1996.4583   6828  0 000
1996.5417   6859  0 000
1996.6250   6905  0 000
1996.7083   6852  0 000
1996.7917   6922  0 000
1996.8750   7053  0 000
1996.9583   6796  0 000
1997.0417   6746  0 000
1997.1250   6919  0 000
1997.2083   6827  0 000
1997.2917   6791  0 000
1997.3750   6810  0 000
1997.4583   6897  0 000
1997.5417   6825  0 000
1997.6250   6874  0 000
1997.7083   6894  0 000
1997.7917   6987  0 000
1997.8750   6879  0 000
1997.9583   6909  0 000
1998.0417   6962  0 000
1998.1250   6910  0 000
1998.2083   6830  0 000
1998.2917   6931  0 000
1998.3750   6825  0 000
1998.4583   6879  0 000
1998.5417   6963  0 000
1998.6250   6915  0 000
1998.7083   6989  0 000
1998.7917   7111  0 000
1998.8750   6925  0 000
1998.9583   6931  0 000

[Jon]

Your script, read_gauges2.m, trys to read the file, student_t_value.dat at line 9. You did not attach the file, student_t_value.dat, so I can not run your code to try to replicate/debug your errors. If you need more help with this, you will need to provide a script and any necessary files needed to replicate the problem.

Also, if this is now a new issue, that is it has nothing to do with the generation of the filenames to be read, then perhaps you should, submit this as a new question. When you do so, please, take some time to identify, exactly what your new question is, and provide an appropriate, self contained (not needed to refer back to this thread) description of the problem and any necessary files to reproduce the problem.

[Ellen]

I cannot add a dat-file but Ive put the data from the file underthe text I wrote. its that statistical thing with t values. You only need it for the rest of the data not for the part to construct the psmsl.mat. Ive run the file only this sector and saved the workspace.

I is in fact the data from this table:

[Jon]

By commenting out the initial lines of read_guages2 and loading your workspace_student_t_valuesector.mat I was able to reproduce your error.

Stepping through the code with the debugger, I see that the problem is here

for jj=startyear:endyear  % go through separate years
    
% annual:

ind_yr=find(year==jj);  % select entries with year jj

gauge.data(stat).annual_level(jj-startyear+1)=mean(level(ind_yr));

If you look at your values at this point, your variable, year, is an integer between 0 and 100, and you are trying to match it with a value of jj which is a value like 1999. So no match is found and ind_yr is empty. Then on the next line you take the mean of level(ind_yr), but since ind_yr is empty, so is level(ind_yr), and taking the mean of an empty value give NaN. So all of your levels are NaN.

So then later when you compute correlations your correlation coefficients are also NaN, and finally when you try to use the index N_eff -2, N_eff is also NaN, and so N_eff-2 is NaN and you get the error.

t_alf=t_0025(N_eff-2);

So you need to clean up the earlier part of your code

% read all entries 
date=alldata(:,1); % in decimal years
year=floor(date);
month=ceil((date-floor(date))*12);
level=alldata(:,2); % in mm

Noting that, at least in the data you gave me, alldata(:,1) is not the date in decimal years, but is in fact just integer values from 0 to 100

[Ellen]

nd_yr=find(year==jj);  % select entries with year jj
gauge.data(stat).annual_level(jj-startyear+1)=mean(level(ind_yr));

you mean I have tot change jj (above txt) to jjjj?

nd_yr=find(year==jjjj);  % select entries with year jj
gauge.data(stat).annual_level(jjjj-startyear+1)=mean(level(ind_yr));

Ellen

[Jon]

I think you are getting confused about working with character vectors, e.g. '1996' and numerical values, 1996.

I'm not totally clear on what you are suggesting here, but it somehow looks like you are thinking that you should compare to jjjj rather than jj to get more digits. If so, then this is not what I meant at all.

Here is the situation.

You first assign a numerical values, (not a character vectors or strings) to your variables date and year, on the lines where you have

date=alldata(:,1); % in decimal years
year=floor(date);

If you look at the values for alldata(:,1), the column you are assigning to date, it is a vector of numerical values (not characters or strings) whose elements are 0, 1, 2, .... 100.

As they do not have any decimal fraction, taking the floor of them leaves them unchanged, so your variable year, is a vector of numerical values (not characters or strings) whose elements are 0,1,2,...100

Next you have a loop in which you assign the loop variable jj, to take on numerical values (not strings or characters) from startyear to endyear which you assigned earlier using

% select years:
startyear=1996;
%startyear=1995; % for plot
endyear=2022;

so as you loop jj wil take on the numerical values 1996,1997,1998,...2022

Inside of the loop you look for the ind_yr (index into the vector of numerical year values) using

ind_yr=find(year==jj);  % select entries with year jj

so you are looking for the element of year where year has a value that matches jj.

Since the elements of year have values, 0,1,2,...101 and, lets say on the first loop, jj = 1996, it clearly will not find any match, there is no element of year that has the value 1996, so it returns empty.

Next you try to compute the mean value of the level corresponding to the ind_yr with right hand side of the line

gauge.data(stat).annual_level(jj-startyear+1)=mean(level(ind_yr));

Since ind_yr is empty, level(ind_yr) is also empty. Since MATLAB doesn't know how to compute the mean of an empty vector, it simple return NaN (which means not a number), and NaN is assigned to

gauge.data(stat).annual_level(jj-startyear+1)

This continues with each successive loop, on the next loop jj =1997, which also is not found in year, which only has value 0,1,2,...101. and again the ind_yr is empty the mean level is NaN until finally all of the values of guage.data(stat).annual_level have been assigned NaN

After that there are no useful results, as you try to compute correlations etc from these vectors of NaN and obviously it can't compute anything useful just using NaN's, and eventually you actually have an error.

So you need to either get your year values to be in the range 1996 to 2022, perhaps by adding your variable called date to some base year. Alternatively you leave the year values as 0,1,2,... and modify the condition you check for a match, so if the year values were, for example, the number of years after 1990, then you could check for

ind_yr = find(year == jj - 1990)

so when, for example jj = 1999, it would give ind_yr = 10, since year(10) has a value of 9 (your year values start at zero) and 1999-1990 equals 9

I hope this helps.