How do you load a .csv file, skip lines within it, and plot the values?

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T 2012-9-21

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Hi. I seem to have problems loading a .csv file (see attached):

 Blah
 @Blah
  2Blah
  Blah
f Blah
 fa Blah
 Blahasd
 Blahasda
vasf Blah
as Blah
asdas Blah
    
     
    
Date  Time  Ch1:
07/25/2012  42:46.0  96.385
07/25/2012  42:46.0  -177.608
07/25/2012  42:46.0  155.481
07/25/2012  42:46.0  64.15

%Here is my code:

fid = fopen('PULL1.CSV');

% I need to skip the 16 lines. header = textscan(fid, '%s',3,'delimiter', ',',... 'headerLines',16);

data = textscan(fid, '%s %s %s' ,'delimiter', ',');

The problem is that it only recognizes the parameters as strings. Date should be a string. Time should be a floating number. The Ch1 column is a set of values that I want to plot vs. time.

fclose(fid);

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T 2012-9-21

Also bare in mind that under column Ch1: the time 42:46.0 represents 5:42:46 PM but I am not sure why Excel automatically displays it as shown in the first post.

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采纳的回答

Walter Roberson 2012-9-21

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在 MATLAB Online 中打开

data_to_plot = str2double(data{3});

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T 2012-9-21

编辑：T 2012-9-21

在 MATLAB Online 中打开

So,

fid = fopen('PULL1.CSV');

% read column headers

header = textscan(fid, '%s',3,'delimiter', ',',... 'headerLines',16);

% read numeric data

data = textscan(fid, '%s %s %s' ,'delimiter', ',');

data_to_plot = str2double(data{3});

datatimes = datenum(data{2}, 'mm:ss.f');

plot(datetimes, data_to_plot);

fclose(fid);

------

Gives the following output:

Error using datenum (line 181) DATENUM failed.

Error in ABL (line 20) datatimes = datenum(data{2}, 'mm:ss.f');

Caused by: Error using dtstr2dtnummx Failed on converting date string to date number.

-------

Nevertheless,

perhaps if I manipulate the data first before I read it, things would be much more subtle:

fid = fopen('PULL1.CSV');

data = textscan(fid, '%s' ,'delimiter', '\b');

data2 = data{:,:}

data3 = data2(13:end,:);

fclose(fid);

-----

The output then is:

'07/25/2012,17:49:56.080,37.288'
  '07/25/2012,17:49:56.085,37.288'
  '07/25/2012,17:49:56.090,53.405'

Would I still have to run textscan to recognize the entries seperated by the commas?

T 2012-9-24

编辑：T 2012-9-24

My x-axis shows the value 7.3487 x10^5 repeatedly. What is the significance of using datenum if what I want is to show the time as it is in the Excel sheet?

Walter Roberson 2012-9-25

Use datetick(). You will want to be selective about which time fields you display, as otherwise the tick labels will run into each other.

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MATLAB Language Fundamentals Data Types Dates and Time

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