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csHjavaA-2019
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revision
traverse and process
standard algorithms
Parallel Arrays
read text files
write text files
CSV files
Letter frequency
development workflow
indices
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CSV file format
the CSV file should contain a values like this
France,Paris
Spain,Madrid
Japan,Tokyo
stored in CSV format with newline character after each line except for the last line
France,Paris\nSpain,Madrid\nJapan,Tokyo
each line is a pair of text values separated by a comma, (there are no spaces)
each line has the same number of values
a CSV file is a standard way of storing a table of values, eg a spreadsheet or database
sometimes the first line will be used as a column heading
there can be 2 or more comma separated values on each line
using one CSV file avoids storing the different values in separate files, all the values can be read or written using one source/destination

A CSV file may contain a values like this (with headings)
Country,Capital,Continent,Population(million)
France,Paris,Europe,66.99
Spain,Madrid,Europe,46.94
Japan,Tokyo,Asia,126.5
reading values from a CSV file into parallel arrays
A Java read operation can read an entire file on a line from a file but not part of a line.
Each CSV line is read from the file as a string which has to be “unpacked” into parallel arrays
"West Lothian,131295"
the comma is a separator between the two values
this long string must be split to give two separate values,
a string for "West Lothian"
an integer for 131295
In this case the data above will be stored in councilName[ ] a string array, and voters[ ] an integer array

split() is a string function that takes a string value and a separator (comma)
// a single string
String[] dataRowA = "West Lothian,131295".split(",");
// an array of two string values
String[] dataRowB = {"West Lothian" , "131295"};
after splitting:
dataRowA[0] contains the string “West Lothian”
dataRowA[1] stores the string “131295”

the values from the array elements are copied to separate string and integer variabl
the string value “131295” is cast (converted) to the integer value 131395

All of the above work is repeated (using a loop) for each line from the file
writing a CSV file from parallel arrays
open file (for writing)
write a line with multiple values separated by commas to the CSV file (in a loop for multiple lines)
fileWriter.print(country[i] + "," + capital[i]);
close the file
CSV file tasks
read from a CSV file
search for array values that match a target value
write only the matching values to a new file
original CSV with all councils
Aberdeen City,145832
Aberdeenshire,192269
Angus,86548
Argyll & Bute,65512
City of Edinburgh,343748
Clackmannanshire,38061
Comhairle Nan Eilean Siar,20979
Dumfries and Galloway,112970
Dundee,104182
East Ayrshire,92593
new CSV file with councils of fewer than 99999 voters
Angus,86548
Argyll & Bute,65512
Clackmannanshire,38061
Comhairle Nan Eilean Siar,20979
East Ayrshire,92593

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