How can I solve this datetick error?

Question

kim le 29 Nov 2023

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Commenté : Peter Perkins le 29 Nov 2023

Réponse acceptée : Star Strider

sea.txt

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attatched file is sea.txt, it will work changing to sea.dat

I'm trying to plot this graph,

however, my graph plots like this.

I'm trying to convert julian date using datetick, but I have no clue what have I done wrong.

xlabel keep goes 01~01

I just need 2019 jan data, so I sliced like that.

clc
clear all
close all
fnm='sea.dat';
fid=fopen(fnm,'r');
data = textscan(fid, '%s%f%f%f%f%f%f%f', 'HeaderLines', 1, 'Delimiter',',');
all = [data{2:8}] ;
atemp = all(1:744,6);
apres = all(1:744,7);
date_str=data{1};
sample_date=date_str(1:744);
j_date=datenum(sample_date);
n_date=datevec(j_date);
x = j_date;
x1 = j_date(1:24:744);
figure
%%
y1 = atemp;
y2 = atemp(1:24:744);
subplot(2,2,[1 2])
plot(x,y1, 'k--')
dateformat = 7;
datetick('x', dateformat)
title('Weather at Observatory')
grid on
hold on
plot(x1,y2,'g*')
xlabel('Date (2019. Jan.)')
ylabel('Air temperature (℃)')
hold off

What have I missed in this case?

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Dyuman Joshi le 29 Nov 2023

Please share the data file you are working with (i.e. sea.dat). Use the paperclip button to attach.

kim le 29 Nov 2023

I fogot about that. I just attached it.

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Answer 1

Star Strider le 29 Nov 2023

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sea.txt

The datetick function uses MATLAB datenum values to calculate and plot the dates and times.

A much simpler approach uis to use the datetime function and the readtable function—

T1 = readtable('sea.txt', 'VariableNamingRule','preserve')

T1 = 8760×8 table

time sea level(cm) wtemp(℃) salinity(PSU) wspd(m/s) wdir(deg) atemp(℃) apres(hPa) ____________________ _____________ ________ _____________ _________ _________ ________ __________ 01-Jan-2019 00:00:00 36.88 7.81 33.54 3.84 256.42 0.13 1030.1 01-Jan-2019 01:00:00 37.93 7.8 33.5 4.98 240.65 -0.5 1029.8 01-Jan-2019 02:00:00 35.83 7.64 33.57 5.64 258.28 -1.14 1029.3 01-Jan-2019 03:00:00 34.95 7.52 33.5 2.81 262.18 -1.37 1029.4 01-Jan-2019 04:00:00 31.73 7.41 33.52 6.4 271.75 -1.7 1028.9 01-Jan-2019 05:00:00 30.92 7.4 33.47 6.51 266.83 -1.86 1028.2 01-Jan-2019 06:00:00 30.33 7.35 33.54 5.84 269.12 -1.81 1028.7 01-Jan-2019 07:00:00 34.8 7.4 33.52 5.58 275.83 -1.67 1028.7 01-Jan-2019 08:00:00 30.87 7.4 33.59 7.05 278.87 -1.64 1029 01-Jan-2019 09:00:00 33.88 7.4 33.5 6.51 272.57 -1.29 1028.5 01-Jan-2019 10:00:00 36.23 7.4 33.56 6.68 262.85 -0.03 1028.2 01-Jan-2019 11:00:00 38.2 7.51 33.56 6.68 272.07 0.88 1027.3 01-Jan-2019 12:00:00 40.22 7.6 33.54 7.08 269.05 1.15 1026.5 01-Jan-2019 13:00:00 41.57 7.64 33.61 8.22 277.1 1.87 1025.3 01-Jan-2019 14:00:00 39.55 7.74 33.56 7.95 279.97 2.42 1025.4 01-Jan-2019 15:00:00 39.82 7.81 33.55 6.88 294.68 2.62 1025.8

VN = T1.Properties.VariableNames;

Lv = (month(T1.time) == 1) & (year(T1.time)== 2019);

% LvHr1 = hour(T1.time) == 1;

Select = T1(Lv,:)

Select = 744×8 table

time sea level(cm) wtemp(℃) salinity(PSU) wspd(m/s) wdir(deg) atemp(℃) apres(hPa) ____________________ _____________ ________ _____________ _________ _________ ________ __________ 01-Jan-2019 00:00:00 36.88 7.81 33.54 3.84 256.42 0.13 1030.1 01-Jan-2019 01:00:00 37.93 7.8 33.5 4.98 240.65 -0.5 1029.8 01-Jan-2019 02:00:00 35.83 7.64 33.57 5.64 258.28 -1.14 1029.3 01-Jan-2019 03:00:00 34.95 7.52 33.5 2.81 262.18 -1.37 1029.4 01-Jan-2019 04:00:00 31.73 7.41 33.52 6.4 271.75 -1.7 1028.9 01-Jan-2019 05:00:00 30.92 7.4 33.47 6.51 266.83 -1.86 1028.2 01-Jan-2019 06:00:00 30.33 7.35 33.54 5.84 269.12 -1.81 1028.7 01-Jan-2019 07:00:00 34.8 7.4 33.52 5.58 275.83 -1.67 1028.7 01-Jan-2019 08:00:00 30.87 7.4 33.59 7.05 278.87 -1.64 1029 01-Jan-2019 09:00:00 33.88 7.4 33.5 6.51 272.57 -1.29 1028.5 01-Jan-2019 10:00:00 36.23 7.4 33.56 6.68 262.85 -0.03 1028.2 01-Jan-2019 11:00:00 38.2 7.51 33.56 6.68 272.07 0.88 1027.3 01-Jan-2019 12:00:00 40.22 7.6 33.54 7.08 269.05 1.15 1026.5 01-Jan-2019 13:00:00 41.57 7.64 33.61 8.22 277.1 1.87 1025.3 01-Jan-2019 14:00:00 39.55 7.74 33.56 7.95 279.97 2.42 1025.4 01-Jan-2019 15:00:00 39.82 7.81 33.55 6.88 294.68 2.62 1025.8

LvHr1 = hour(Select.time) == 1;

figure

plot(Select{:,1}, Select{:,7}, '--k')

hold on

plot(Select{LvHr1,1}, Select{LvHr1,7}, 'g*')

hold off

grid

xlabel(VN{1})

ylabel(VN{7})

.

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Star Strider le 29 Nov 2023

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sea.txt

You can calculate ‘Lv’ using column references (note the use of curly braces {}) rather than variable names:

Lv = (month(data{:,1}) == 1) & (year(data{:,1}) == 2019);

Also, you can rrefer to the variablle names by reference to the ‘VN’ cell array, as I do here.

data = readtable('sea.txt', 'VariableNamingRule','preserve')

data = 8760×8 table

time sea level(cm) wtemp(℃) salinity(PSU) wspd(m/s) wdir(deg) atemp(℃) apres(hPa) ____________________ _____________ ________ _____________ _________ _________ ________ __________ 01-Jan-2019 00:00:00 36.88 7.81 33.54 3.84 256.42 0.13 1030.1 01-Jan-2019 01:00:00 37.93 7.8 33.5 4.98 240.65 -0.5 1029.8 01-Jan-2019 02:00:00 35.83 7.64 33.57 5.64 258.28 -1.14 1029.3 01-Jan-2019 03:00:00 34.95 7.52 33.5 2.81 262.18 -1.37 1029.4 01-Jan-2019 04:00:00 31.73 7.41 33.52 6.4 271.75 -1.7 1028.9 01-Jan-2019 05:00:00 30.92 7.4 33.47 6.51 266.83 -1.86 1028.2 01-Jan-2019 06:00:00 30.33 7.35 33.54 5.84 269.12 -1.81 1028.7 01-Jan-2019 07:00:00 34.8 7.4 33.52 5.58 275.83 -1.67 1028.7 01-Jan-2019 08:00:00 30.87 7.4 33.59 7.05 278.87 -1.64 1029 01-Jan-2019 09:00:00 33.88 7.4 33.5 6.51 272.57 -1.29 1028.5 01-Jan-2019 10:00:00 36.23 7.4 33.56 6.68 262.85 -0.03 1028.2 01-Jan-2019 11:00:00 38.2 7.51 33.56 6.68 272.07 0.88 1027.3 01-Jan-2019 12:00:00 40.22 7.6 33.54 7.08 269.05 1.15 1026.5 01-Jan-2019 13:00:00 41.57 7.64 33.61 8.22 277.1 1.87 1025.3 01-Jan-2019 14:00:00 39.55 7.74 33.56 7.95 279.97 2.42 1025.4 01-Jan-2019 15:00:00 39.82 7.81 33.55 6.88 294.68 2.62 1025.8

VN = data.Properties.VariableNames;

Lv = (month(data{:,1}) == 1) & (year(data{:,1}) == 2019);

% LvHr1 = hour(data{:,1}) == 1;

Select = data(Lv,:)

Select = 744×8 table

time sea level(cm) wtemp(℃) salinity(PSU) wspd(m/s) wdir(deg) atemp(℃) apres(hPa) ____________________ _____________ ________ _____________ _________ _________ ________ __________ 01-Jan-2019 00:00:00 36.88 7.81 33.54 3.84 256.42 0.13 1030.1 01-Jan-2019 01:00:00 37.93 7.8 33.5 4.98 240.65 -0.5 1029.8 01-Jan-2019 02:00:00 35.83 7.64 33.57 5.64 258.28 -1.14 1029.3 01-Jan-2019 03:00:00 34.95 7.52 33.5 2.81 262.18 -1.37 1029.4 01-Jan-2019 04:00:00 31.73 7.41 33.52 6.4 271.75 -1.7 1028.9 01-Jan-2019 05:00:00 30.92 7.4 33.47 6.51 266.83 -1.86 1028.2 01-Jan-2019 06:00:00 30.33 7.35 33.54 5.84 269.12 -1.81 1028.7 01-Jan-2019 07:00:00 34.8 7.4 33.52 5.58 275.83 -1.67 1028.7 01-Jan-2019 08:00:00 30.87 7.4 33.59 7.05 278.87 -1.64 1029 01-Jan-2019 09:00:00 33.88 7.4 33.5 6.51 272.57 -1.29 1028.5 01-Jan-2019 10:00:00 36.23 7.4 33.56 6.68 262.85 -0.03 1028.2 01-Jan-2019 11:00:00 38.2 7.51 33.56 6.68 272.07 0.88 1027.3 01-Jan-2019 12:00:00 40.22 7.6 33.54 7.08 269.05 1.15 1026.5 01-Jan-2019 13:00:00 41.57 7.64 33.61 8.22 277.1 1.87 1025.3 01-Jan-2019 14:00:00 39.55 7.74 33.56 7.95 279.97 2.42 1025.4 01-Jan-2019 15:00:00 39.82 7.81 33.55 6.88 294.68 2.62 1025.8

LvHr1 = hour(Select{:,1}) == 1;

figure

plot(Select{:,1}, Select{:,7}, '--k', 'DisplayName',VN{7})

hold on

plot(Select{LvHr1,1}, Select{LvHr1,7}, 'g*', 'DisplayName',[string(VN{7})+" 01:00"])

hold off

grid

xlabel(VN{1})

ylabel(VN{7})

legend('Location','best')

.

Star Strider le 29 Nov 2023

As always, my pleasure!

Peter Perkins le 29 Nov 2023

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All of that is good stuff, but these data cry out for a timetable, i.e. the readtimetable function. Everything else stays more or less that same, but when you are done plotting against time, you may find that a timetable makes the other things you want to do easier.

T1 = readtimetable("https://www.mathworks.com/matlabcentral/answers/uploaded_files/1555502/sea.txt", VariableNamingRule="preserve")
T1 = 8760×7 timetable
            time            sea level(cm)    wtemp(℃)    salinity(PSU)    wspd(m/s)    wdir(deg)    atemp(℃)    apres(hPa)
    ____________________    _____________    ________    _____________    _________    _________    ________    __________

    01-Jan-2019 00:00:00        36.88          7.81          33.54          3.84        256.42        0.13        1030.1  
    01-Jan-2019 01:00:00        37.93           7.8           33.5          4.98        240.65        -0.5        1029.8  
    01-Jan-2019 02:00:00        35.83          7.64          33.57          5.64        258.28       -1.14        1029.3  
    01-Jan-2019 03:00:00        34.95          7.52           33.5          2.81        262.18       -1.37        1029.4  
    01-Jan-2019 04:00:00        31.73          7.41          33.52           6.4        271.75        -1.7        1028.9  
    01-Jan-2019 05:00:00        30.92           7.4          33.47          6.51        266.83       -1.86        1028.2  
    01-Jan-2019 06:00:00        30.33          7.35          33.54          5.84        269.12       -1.81        1028.7  
    01-Jan-2019 07:00:00         34.8           7.4          33.52          5.58        275.83       -1.67        1028.7  
    01-Jan-2019 08:00:00        30.87           7.4          33.59          7.05        278.87       -1.64          1029  
    01-Jan-2019 09:00:00        33.88           7.4           33.5          6.51        272.57       -1.29        1028.5  
    01-Jan-2019 10:00:00        36.23           7.4          33.56          6.68        262.85       -0.03        1028.2  
    01-Jan-2019 11:00:00         38.2          7.51          33.56          6.68        272.07        0.88        1027.3  
    01-Jan-2019 12:00:00        40.22           7.6          33.54          7.08        269.05        1.15        1026.5  
    01-Jan-2019 13:00:00        41.57          7.64          33.61          8.22         277.1        1.87        1025.3  
    01-Jan-2019 14:00:00        39.55          7.74          33.56          7.95        279.97        2.42        1025.4  
    01-Jan-2019 15:00:00        39.82          7.81          33.55          6.88        294.68        2.62        1025.8  

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