How do i reset a fileID value?

Relatively new to MATLAB so it's probably a stupid question. But when writing my code I forgot to use the fclose function in my for loop so the value kept going up. My fid value i believe should be 34 but shows as 54 (my dataset has 34 colums). How do I sort of reset my fid value? also if anyone spots anything else wrong with the code that would be great. This is only a small portion of the code as I am just trying to get this part to work first.

close all
clear all
clc

fpath=uigetdir;
files=dir([fpath '\*.csv']);
files=char(files.name);

for n=1:size(files,1)
    fid=fopen([fpath '\' files(n,:)]);
    data{n}=textscan(fid, '%s %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f','Delimiter',',','CollectOutput',1, 'Headerlines',1);
    fclose(fid);
    data{1,n}{1,1}=datenum(data{1,n}{1,1},'dd-mmm-yyyy HH:MM:SS');
end

[Stephen23]

Some tips on looping over filenames:

fpath = uigetdir;
files = dir(fullfile(fpath,'*.csv')); % use FULLFILE rather than text concatenation.
for n = 1:numel(files) % no need for a char array...
     fnm = fullfile(fpath,files(n).name); % ... you can access the structure directly.
     ...
     files(n).data  = ... optional, if you want to store any data
 end

As Image Analyst wrote in your other answer, you should not convert the filenames into a character array.

Answer 1

[Star Strider]

Using:

fclose('all')

should close all of them. You can then start with fid = 3.

Also, I lost count of the number of '%f' there are. You can avoid writing all that with:

['%s' repmat('%f', 1, 33)]

ans = '%s%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f%f'

And I don’t understand using datenum here:

data{1,n}{1,1}=datenum(data{1,n}{1,1},'dd-mmm-yyyy HH:MM:SS');

The datetime function allows for sorting, comparisons, logical operations, and a number of others.

.

[Whale_Shark]

Thank you for your reply, you're an absolute star. With the datenum section, the first column of my data has the Date/Time (GMT) written as say

01-Jan-2015 02:30:00

so im trying to use a function to allow matlab to be able to read the data and was suggested the code above. How would I use the datetime function in this case?

[Star Strider]

As always, my pleasure!

I very much appreciate yoiur compliment!

I would do something like this —

str = '01-Jan-2015 02:30:00';
datetime(str, 'InputFormat','dd-MMM-yyyy HH:mm:ss')         % NOTE — Format Differences

ans = datetime
   01-Jan-2015 02:30:00

Or since there appears to be no ambiguity in the dates or times, simply —

datetime(str)

ans = datetime
   01-Jan-2015 02:30:00

Also, if you use readtable, it should do the conversion for you automatically, as well as retain the column header data (variable names) that you can then reference.

It would help to know what version/release you’re using, since there have been changes in the last few releases.

.

[Whale_Shark]

Hi! Thanks again for the speedy reply! The version of matlab I'm using is MATLAB R2022b. Basically the data that I am using is annual data from 1st Jan to 31st Dec and is im my data as shown:

Date/Time (GMT)

01-Jan-2015 00:00:00

01-Jan-2015 00:30:00

01-Jan-2015 01:00:00

01-Jan-2015 01:30:00

01-Jan-2015 02:00:00

01-Jan-2015 02:30:00

...and so on...

It is the first column of 34. I am working with ocean wave parameter data and need to create a FOR LOOP as I am comparing 5 years of data from two sites (each year is its down .csv data file). What I am aiming to achieve in this part of the code is that it can read all of the Date/Time (GMT) column data in the format as I will be needing to plot parameters such as wave height against time and such. I just can't seem to get it to be able to read the time data.

Thank you for all your help once again, its saving me from stress :D.

[Star Strider]

I’m not certain what the problem could be. The ‘Date/Time (GMT)’ data should be automatically converted to a datetime array, since there appears to be no ambiguity, although it might require adding 'TimeZone','UTC'. It would help if you could attach one of your data files.

[Whale_Shark]

Here is one of the data files that i am working with. Each year is a different file, so I have five files from 2015 to 2019 for this site. Im having trouble getting it to read the data so I can't generate my variables for data such as wave height in MATLAB.

[Star Strider]

The readtable funciton imports the first column automatically as a datetime array, although it doesn’t have an associated 'TimeZone' property, so I set it to 'UTC'.

Assuming that ‘Hmax’ is the maximum wave height, I have no problems retrieving it and plotting it. (Plotting all of them reveals wave heights of 10000 meters, so I assumes that codes for missing data, since a wave height of that amplitude would be notable!)

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1207193/GdS_allwaveparameters2015.csv', 'VariableNamingRule','preserve')

T1 = 17520×34 table
      Date/Time (GMT)       Latitude    Longitude    Percentage of waves    Hmax (m)    Tmax (s)    H1/10 (m)    T1/10 (s)    H1/3 (m)    T1/3 (s)     Hav     Tav     Eps     Number of waves    Tp (s)    Direction (deg)    Spread (deg)    Tm02 (Tm)(s)    Hm0 (Hs)(m)    TI (s)    T1 (s)    Tc (s)    Tdw2 (s)    Tdw1 (s)    Tpc (s)     nu       eps      QP      Ss      Tref (deg C)    SST (deg C)    battery    Te (s)    P (kW/m2)
    ____________________    ________    _________    ___________________    ________    ________    _________    _________    ________    ________    _____    ___    _____    _______________    ______    _______________    ____________    ____________    ___________    ______    ______    ______    ________    ________    _______    _____    _____    ____    _____    ____________    ___________    _______    ______    _________

    01-Jan-2015 00:00:00      51.25      1.4832              100              1.46        4.7         1.07          4.5         0.87        4.5        0.55    3.8    0.515          469           5.6            184               10               4            0.99         4.9       4.3       3.1        4.5         5.7         5.7      0.356    0.642    2.49     0.04        9999           9999         9999       4.7        2.26   
    01-Jan-2015 00:30:00      51.25      1.4832              100              1.89        4.9         1.08          4.8         0.86        4.8       0.561    4.2     0.59          437           4.3            191               21             3.8            0.97         4.6         4         3        4.2         4.8         5.4       0.35    0.618    2.08    0.044        25.1            8.3            1       4.4        2.04   
    01-Jan-2015 01:00:00      51.25      1.4833              100              1.48        5.3         1.15          5.1         0.94        5.1       0.605    4.5    0.584          401           5.9            183               12             4.1            1.04         4.9       4.3       3.1        4.5         5.5         5.7      0.344    0.634    2.35     0.04        25.1            8.2            1       4.7         2.5   
    01-Jan-2015 01:30:00      51.25      1.4826              100              1.68        5.6         1.19          5.4         0.95        5.3         0.6    4.6    0.605          391           5.9            186               12             4.3            1.03         5.1       4.5       3.3        4.7           6         5.9      0.336     0.62    2.52    0.036        25.1            8.2            1       4.9        2.55   
    01-Jan-2015 02:00:00      51.25      1.4825              100              2.36          6         1.38          5.5         1.08        5.7       0.673    4.9    0.543          367           6.3            186               16             4.7            1.12         5.5       4.9       3.6        5.1         7.2         6.2      0.329    0.638    3.02    0.032        25.1            8.1            1       5.3        3.27   
    01-Jan-2015 02:30:00      51.25      1.4825              100              2.74        5.5         1.62          5.7         1.27        5.7       0.796      5    0.552          362           6.3            177               18             4.6            1.13         5.5       4.9       3.6        5.1         6.3         6.3      0.332    0.628    2.45    0.034        25.1            8.1            1       5.3        3.33   
    01-Jan-2015 03:00:00      51.25      1.4825              100              2.49        6.2         1.63          6.2         1.29        6.3       0.822    5.3    0.565          339           6.7            176               16               5             1.4         5.8       5.2         4        5.4         7.6         6.5      0.305    0.616    3.14    0.036        25.1              8            1       5.6        5.39   
    01-Jan-2015 03:30:00      51.25      1.4823              100              2.45        6.1         1.63          6.2         1.25        6.3       0.797    5.4    0.545          332           6.7            172               15             5.3            1.47         6.1       5.6       4.1        5.7         8.8         6.7      0.306    0.631    3.73    0.033        25.1              8            1       5.8        6.15   
    01-Jan-2015 04:00:00      51.25      1.4823              100              1.85        6.4         1.35          6.1         1.08        6.1       0.683    5.3    0.598          343           6.7            174               15             4.9            1.15         5.9       5.2       3.7        5.4         7.3         6.7      0.354    0.664    2.69    0.031        25.1            7.9            1       5.6        3.64   
    01-Jan-2015 04:30:00     51.249      1.4823              100              2.18        5.7         1.18            6         0.92        5.7        0.58    4.6    0.605          391           6.7            176               15             4.2            1.02         5.5       4.6       3.1        4.9         6.9         6.6      0.414    0.682    2.53    0.036        9999           9999         9999       5.2        2.66   
    01-Jan-2015 05:00:00      51.25      1.4823              100              1.44        5.9         1.11          5.6         0.93        5.6        0.59    4.5    0.631          402           6.7            176               14             4.1            0.96         5.5       4.5       2.8        4.9         7.3         6.7      0.464    0.726    2.78    0.037        9999           9999         9999       5.3        2.41   
    01-Jan-2015 05:30:00      51.25      1.4823              100              1.51        5.7         1.09          5.8         0.89        5.8        0.55    4.4    0.656          412           6.3            180               18             4.2            0.92         5.5       4.6       2.8        4.9         7.5         6.5      0.452    0.742    3.15    0.033        9999           9999         9999       5.2        2.17   
    01-Jan-2015 06:00:00      51.25      1.4824              100              1.89        5.9         1.18          5.7         0.94        5.7        0.59    4.7     0.68          385           6.3            188               20             4.4            1.45         5.3       4.7       3.2          5         7.1           6       0.37     0.69    3.17    0.047        9999           9999         9999       5.3        5.49   
    01-Jan-2015 06:30:00      51.25      1.4828              100              2.56        5.4         1.67          5.5         1.34        5.4        0.88    4.8    0.617          377           5.3            186               16               4            1.49           5       4.2       2.9        4.5         5.8         5.8      0.386     0.67    2.49    0.061        9999           9999         9999       4.8        5.25   
    01-Jan-2015 07:00:00      51.25      1.4828              100              2.48        4.9         1.68            5          1.3          5        0.82      4    0.583          446           5.9            188               24             3.8            1.43         4.8       4.1       2.9        4.3         5.4         5.7      0.382    0.648     2.2    0.062        9999           9999         9999       4.5        4.52   
    01-Jan-2015 07:30:00      51.25      1.4828              100              2.22        4.5         1.65            5          1.3        4.9        0.84      4    0.578          447           5.6            190               18             3.7            1.55         4.8         4       2.8        4.3         5.2         5.8      0.397    0.662    2.09    0.071        9999           9999         9999       4.6        5.45   

VN = T1.Properties.VariableNames;
DT = T1.('Date/Time (GMT)')

DT = 17520×1 datetime array
   01-Jan-2015 00:00:00
   01-Jan-2015 00:30:00
   01-Jan-2015 01:00:00
   01-Jan-2015 01:30:00
   01-Jan-2015 02:00:00
   01-Jan-2015 02:30:00
   01-Jan-2015 03:00:00
   01-Jan-2015 03:30:00
   01-Jan-2015 04:00:00
   01-Jan-2015 04:30:00
   01-Jan-2015 05:00:00
   01-Jan-2015 05:30:00
   01-Jan-2015 06:00:00
   01-Jan-2015 06:30:00
   01-Jan-2015 07:00:00
   01-Jan-2015 07:30:00
   01-Jan-2015 08:00:00
   01-Jan-2015 08:30:00
   01-Jan-2015 09:00:00
   01-Jan-2015 09:30:00
   01-Jan-2015 10:00:00
   01-Jan-2015 10:30:00
   01-Jan-2015 11:00:00
   01-Jan-2015 11:30:00
   01-Jan-2015 12:00:00
   01-Jan-2015 12:30:00
   01-Jan-2015 13:00:00
   01-Jan-2015 13:30:00
   01-Jan-2015 14:00:00
   01-Jan-2015 14:30:00

T1.('Date/Time (GMT)').TimeZone = 'UTC';                        % Set 'TimeZone' Property
T1.('Date/Time (GMT)').TimeZone                                 % Check

ans = 'UTC'

figure
plot(T1.('Date/Time (GMT)'), T1.('Hmax (m)'))                   % Variable Name Reference
grid
xlim([0  hours(24)]+T1{1,1})
xlabel(VN{1})
ylabel(VN{5})
title('First 24 Hours Hmax')

figure
plot(T1{:,1}, T1{:,5})                                          % Column Index Reference
grid
xlim([0  hours(24)]+T1{1,1})
xlabel(VN{1})
ylabel(VN{5})
title('First 24 Hours Hmax')

This would likely require the Mapping Toolbox to plot with respect to the geographic coordinates. Since I don’t have it (and so have very little experience with it other than here on Answers), I defer to you for that.

.

[Whale_Shark]

You are a saint, thank you.

[Star Strider]

As always, my pleasure!

[Whale_Shark]

Just seen your other comment on the other question. Thanks again for all your help!

[Whale_Shark]

Good person, it seems i require your assistance once again. So I was typing in the code line by line just to see if I typed it in correctly but now I get the error code:

Dot indexing is not supported for variables of this type.

Here is what I've typed in:

close all
 clear all
 clc
 
 %Load in the data

 fpath=uigetdir;
 files=dir([fpath '\*.csv']);
 files=char(files.name);

 %for loop to go through the variable files, creating variables for wave
 %height (Hmax [H])), max period (Tmax [T]), and geographical direction in
 %degrees (Directiondeg [direction]). Using textscan function to read the
 %data files.

 for n=1:size(files,1)
     fid=fopen([fpath '\' files(n,:)]);
     data{n}=textscan(fid, ['%s' repmat('%f', 1,34)],'Delimiter',',','CollectOutput',1, 'Headerlines',1);
     fclose(fid);
     %readmatrix to set datetime array for first column in the data.
     T1=readmatrix([fpath '\' files(n,:)]);
     VN=T1.Properties.VariableNames;
     DT=T1.('Date\Time (GMT)');
     T1.('Date\Time (GMT)').TimeZone='UTC';
     T1.('Date\Time (GMT)').TimeZone
 end

It produces T1 and the data is there, but the time column shows as NaN due to the dot indexing error.

[Star Strider]

The first instance I see of any dot indexing is in the ‘VN’ assignment. My code uses readtable, not readmatrix. Use readtable instead and see if the error persists.

Check to see what ‘T1’ is after that assignment. It should be a table and the rest of the code should then work correctly.

(Otherwise, it is possible that the file itself was not actually read, so ‘T1’ is empty.)

[Whale_Shark]

So the readmatrix was me being an idiot and not realising that i had typed readmatrix instead of readtable. It now produces the variables with the headers VN and T1 with the data values (see imported picture below),

but produces a warning and anothe error (see imported picture below).

close all
 clear all
 clc
 
 %Load in the data

 fpath=uigetdir;
 files=dir([fpath '\*.csv']);
 files=char(files.name);

 %for loop to go through the variable files, creating variables for wave
 %height (Hmax [H])), max period (Tmax [T]), and geographical direction in
 %degrees (Directiondeg [direction]). Using textscan function to read the
 %data files.

 for n=1:size(files,1)
     fid=fopen([fpath '\' files(n,:)]);
     data{n}=textscan(fid, ['%s' repmat('%f', 1,34)],'Delimiter',',','CollectOutput',1, 'Headerlines',1);
     fclose(fid);
     %readtable to set datetime array for first column in the data.
     T1=readtable([fpath '\' files(n,:)]);
     VN=T1.Properties.VariableNames;
     DT=T1.('Date/Time (GMT)');
     T1.('Date/Time (GMT)').TimeZone='UTC';
     T1.('Date/Time (GMT)').TimeZone
 end
 

[Star Strider]

It’s not an error, simply a Warning.

My original code solves that as well:

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1207193/GdS_allwaveparameters2015.csv', 'VariableNamingRule','preserve')

→ → → → → ↑

Follow the arrows to the solution.

.

[Whale_Shark]

You, Star Strider, are a heaven sent angel (other good beings and planes of existance are available). Seriously, thank you for all your help!!!

[Star Strider]

As always, my pleasure!

Answer 2

[Image Analyst]

@Victoria Snell regarding your dot indexing problem, did you not see my Answer in your duplicate question:

https://www.mathworks.com/matlabcentral/answers/1863168-index-in-position-2-exceeds-array-bounds-index-must-not-exceed-2#answer_1111853

I show you how to fix that by creating the filename properly.