How to plot date on x-axis when it is retrieved as 'text' from table.

I want to plot time series from a .txt file. After importing the file as attached sample.txt. I run the following code to read the 5th and the 7th column. I am facing problem in retrieving the 'date' given in 5th column so that I can plot a scatter plot. The x-label should like 2013 2014 2015 ....

I would be grateful if you can help to resolve my issue.

data=sample;
[a,b]=size(data);
j=1;
n=500;
d=zeros(n,1); %Problem
for i=1:a
    if strcmp("AREQ",data.SITE(i,1))
        x(j)=data{i,7};
        d(j)=datetime(data{i,5},'InputFormat','yyyy-MM-dd'); %Problem
        j=j+1;
    end
end
%% Plotting
A=x(1:j-1,:);
D=datetime(d(1:j-1,:));
figure;
scatter(D,A); % Problem...The x-axis should be in year 2013 2014 2015 ..

Thank you

Answer 1

[Star Strider]

The readtable function imports it as a datetime array —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1113585/sample.txt')

T1 = 67×21 table
      Var1      Var2     Var3    Var4       Var5       Var6        Var7           Var8        Var9     Var10     Var11       Var12       Var13      Var14       Var15          Var16          Var17       Var18     Var19       Var20       Var21  
    ________    _____    ____    ____    __________    _____    ___________    __________    ______    _____    ________    ________    ________    _____    ___________    ___________    ___________    _____    ________    ________    ________

    {'AREQ'}    56301    2013      9     2013-01-09    {'|'}     2.6245e+06    4.6466e+07    792.29    {'|'}    0.006992    0.002125    0.005306    {'|'}    -2.7134e+05     5.8364e+06     2.5514e+06    {'|'}    0.002116    0.004828    0.007333
    {'AREQ'}    56302    2013     10     2013-01-10    {'|'}     2.6245e+06    4.6466e+07    792.28    {'|'}    0.007329    0.002045    0.005595    {'|'}    -2.7134e+05     5.8364e+06     2.5514e+06    {'|'}    0.002034    0.005107     0.00768
    {'AREQ'}    56303    2013     11     2013-01-11    {'|'}     2.6245e+06    4.6466e+07    792.28    {'|'}    0.007111    0.001963    0.005342    {'|'}    -2.7134e+05     5.8364e+06     2.5514e+06    {'|'}    0.001953    0.004836    0.007467
    {'AREQ'}    56304    2013     12     2013-01-12    {'|'}     2.6245e+06    4.6466e+07    792.28    {'|'}    0.007199     0.00199    0.005435    {'|'}    -2.7134e+05     5.8364e+06     2.5514e+06    {'|'}    0.001978    0.004932    0.007555
    {'AREQ'}    57531    2013    144     2013-05-23    {'|'}     2.6245e+06    4.6466e+07    792.29    {'|'}    0.007362    0.001667    0.005361    {'|'}    -2.7134e+05     5.8364e+06     2.5514e+06    {'|'}    0.001654    0.004773    0.007759
    {'AREQ'}    56293    2013      1     2013-01-01    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007153    0.002007    0.004971    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001317    0.004951    0.007326
    {'AREQ'}    56294    2013      2     2013-01-02    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007185    0.002028    0.005038    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001319    0.005028    0.007355
    {'AREQ'}    56295    2013      3     2013-01-03    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007039    0.001971    0.004903    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001283    0.004886    0.007208
    {'AREQ'}    56296    2013      4     2013-01-04    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007311    0.001979    0.004904    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001314    0.004844    0.007498
    {'AREQ'}    56297    2013      5     2013-01-05    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007211    0.002011     0.00493    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001347    0.004891     0.00739
    {'AREQ'}    56298    2013      6     2013-01-06    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007641    0.002071    0.005183    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001347    0.005134    0.007833
    {'AREQ'}    56299    2013      7     2013-01-07    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007715    0.002148    0.005241    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001452    0.005191    0.007908
    {'AREQ'}    56300    2013      8     2013-01-08    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.008008    0.002159    0.005381    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001419    0.005319    0.008212
    {'AREQ'}    56301    2013      9     2013-01-09    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}     0.00731    0.002007     0.00491    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001357    0.004851    0.007496
    {'AREQ'}    56302    2013     10     2013-01-10    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007659    0.002114    0.005191    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001417    0.005139    0.007851
    {'AREQ'}    56303    2014     11     2014-01-11    {'|'}    -1.8221e+06    1.9234e+07    2488.9    {'|'}    0.007443    0.002034     0.00495    {'|'}     1.9428e+06    -5.8041e+06    -1.7969e+06    {'|'}    0.001391    0.004877    0.007636

T1.Var5                                             % Check

ans = 67×1 datetime array
   2013-01-09
   2013-01-10
   2013-01-11
   2013-01-12
   2013-05-23
   2013-01-01
   2013-01-02
   2013-01-03
   2013-01-04
   2013-01-05
   2013-01-06
   2013-01-07
   2013-01-08
   2013-01-09
   2013-01-10
   2014-01-11
   2014-01-12
   2014-01-13
   2014-01-14
   2014-01-15
   2014-01-16
   2014-01-17
   2014-01-18
   2015-01-19
   2015-01-20
   2015-01-21
   2015-01-22
   2015-01-23
   2015-01-24
   2015-01-25

SelectRows = strcmp(T1.Var1,'AREQ');

figure
scatter(T1.Var5(SelectRows), T1.Var7(SelectRows))

% xlim([datetime(2013,01,01) datetime(2014,01,01)])

The loop is not necessary.

.

[Sujata Dhar]

Perfect, thank you :)

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

.

[Sujata Dhar]

Okay, I have another small query over it. If I want to just display years in x axis label, then what's the function for it.

[Sujata Dhar]

years in 'yyyy' format.

[Star Strider]

It does that automatically here. Otherwise, use the xtickformat (introduced in R2016b) function, specifically:

xtickformat('yyyy')

There is more information and related functions in the See Also section of that documentation.

[Sujata Dhar]

Thank you :)

[Star Strider]

As always, my pleasure!

[Sujata Dhar]

How can I plot trendline on this scatter plot. As I am trying with lsline. But error prompts in with

Check for incorrect argument data type or missing argument in call to function 'isnan'.

[Star Strider]

The lsline function apparently doesn’t like datetime variables, so use polyfit and polyval (with modifications) instead — .

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1113585/sample.txt');
% T1.Var5                                             % Check

SelectRows = strcmp(T1.Var1,'AREQ');

figure
scatter(T1.Var5(SelectRows), T1.Var7(SelectRows))
[B,S,mu] = polyfit(datenum(T1.Var5(SelectRows)), T1.Var7(SelectRows),1);    % Use 'datenum' & Centreing & Scaling
ls = polyval(B,datenum(T1.Var5(SelectRows)),S,mu);                          % Evaluate
hold on
plot(T1.Var5(SelectRows), ls, '-r')                                         % Plot Trend Line
hold off

% xlim([datetime(2013,01,01) datetime(2014,01,01)])

They apparently do not like datetime variables either, however it is possible to deceive them (using datenum) to get a reasonable result. The advantage to this approach is that it is not necessarily restricted to a linear fit, and can accommodate higher-order polynomials if desired.

.

[Sujata Dhar]

Thank you very much :) Let me try.

[Sujata Dhar]

It worked. Thank you so much. I have been looking for answers from long. :) :)

Have a wonderful weekend

[Star Strider]

As always, my pleasure!

You, too!