1. Jeff Henrikson (jhenriks@umd.edu)
Lecture 12
Program Improvement
Jeff Henrikson 1

2. Import/Export ASCII File
ASCII File with Known Data Format:
Import Export
csvread
dlmread
textscan
textread
fscanf
csvwrite
dlmwrite
Cell Array
{..} – access
cellplot – visualize
celldisp – display
Parentheses ( ) Square brackets [ ] Curly brackets { } Angle brackets or chevrons ⟨ ⟩ Corner and half brackets ｢｣, ⌊ ⌋ Double brackets ⟦ ⟧
File with Unknown Data Format:
uiimport Import Wizard
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3. Atmospheric Sounding Open Explorer & go to http://weather.uwyo.edu
Navigate to Upper Air Observations  Soundings
From the menu select
Region: North America
Type of plot: Text List
Year:
Month: Jul
From: 15/12Z
To: 15/12Z
Find Sterling VA (IAD) on the map and click
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4. Do not forget the quotes
urlread
Copy & Paste urlname here
Two fingers click on the page and choose View Page Source
Type in the Command Window
>> a = urlread ('
Do not forget the quotes
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5. urlread urlread reads all characters in the source file
Source file contains data and formatting text
We need only the data not the formatting text
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6. urlread a is an array of thousands of characters!
We have to locate the actual data within a
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7. Locate Data Start & End Data are bound by delimiters Scroll down
Search for delimiters: strfind, regexp, strtok, etc.
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8. String Find / Length
Position=533
Position=610
Linefeed
>>L1 = ' ';
>>Id = length(L1)+1; % length of 1st data line =78
>>Ib = strfind(a, L1); % position of 1st char =533
>>Ie = Ib + Id-1; % position of last char =610
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9. Get Data Structure Start End Line 1 533 610 Line 2 611 687 
>> Je = strfind (a,'</PRE>'); % data bound
>> Ix = Je(1)-1; % last data char = 9892
>> Ln = (Ix-Ib+1)/Id; % total num of data lines = 120
for l = 1:Ln
i1 = Ib+(l-1)*Id; i2 = i1+Id;
disp (a(i1:i2))
end
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10. Convert String to Data
We can read multiple lines and convert each line into a 1-d array
>> b = str2num ( a (i1:i2) )
We need to convert the whole table into a 2-d array
# of rows = num of data lines to read
# of columns = num of data fields (=11)
>> if length ( b ) < 11 indicate missing data => ignore the line
Missing data
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11. Final Code Save this code into an M-File called L12E1.m
close; clear; clc
a = urlread('
L1 =' ';
Id = length(L1)+1; % length of 1st data line
Ib = strfind(a, L1); % position of 1st char
Ie = Ib + Id-1; % position of last char
Je = strfind (a,'</PRE>'); % data bound
Ix = Je(1)-1; % last data char
Ln = (Ix-Ib+1)/Id; % total no of data lines
Fn = 11; % no of fields
Rn = 0; % no of valid data records
for l = 1:Ln
i1 = Ib+(l-1)*Id; i2 = i1+Id;
b = str2num (a(i1:i2));
if (length(b)==Fn) % add the data if no missing
Rn = Rn+1;
z(Rn,:) = b(:);
end
disp([z(:,1),z(:,Fn)]); % for visual validation
plot( z(:,3), z(:,1) ); set(gca, 'ydir','rev');
title('Sounding at Sterling'); xlabel('Temperature (C)'); ylabel('Pressures (hPa)');
Final Code
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