How would I go about adding a new column to a CSV file, and adding caluculated data in each column?
example
userid,expDate
1,012015
2,022016
3,032018
I would take expDate from each row, calculate it relative to current month and year to get how many months till it expires, then round monthsTill (so monthsTill of next month will be 1, regardless if its the 1st day or last day of the current month)
userid,expDate,monthsTill
1,022017,0
2,032017,1
3,042017,2
3,052017,3
also how would you "skip" rows that have a certain value in there respective columns?
Based on your pseudo code, here is what should do the trick
private void process(){
BufferedReader bufferedReader = null;
PrintWriter p = null;
String sep = ",";
String newCol = "monthsTill";
String defaultTillExpMonth = ">3";
Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
int currMonth = cal.get(Calendar.MONTH) + 1;
try {
// read csv file
List<String> input = new ArrayList<String>();
File inputFile = new File("InputFile");
bufferedReader = new BufferedReader(new FileReader(inputFile));
String readLine = "";
while ((readLine = bufferedReader.readLine()) != null) {
input.add(readLine);
}
// for each row after first row
// calculate timeTillExpired
// if format MYYYY (ex 22017)
// M and YYYY -> MM and YYYY
// calculate relative to current date as months
int numOfRecords = input.size();
if(numOfRecords>1){
List<String> output = new ArrayList<String>();
String header = input.get(0) +sep +newCol;
output.add(header);
// for each row after first row
// calculate timeTillExpired
// if format MYYYY (ex 22017)
// M and YYYY -> MM and YYYY
// calculate relative to current date as months
for(int i=1;i<numOfRecords;i++){
// I am simply going to get the last column from record
String row = input.get(i);
StringBuilder res = new StringBuilder(row);
String [] entries = row.split(sep);
int length = entries.length;
if(length>0){
res.append(sep);
String rec = entries[length-1];
int expMonth = 0;
// Case of MYYYY. Assumption is it's either MYYYY or MMYYYY
if(rec.length()==5){
expMonth = Integer.valueOf(rec.substring(0, 1));
} else {
expMonth = Integer.valueOf(rec.substring(0, 2));
}
int monToExp = expMonth - currMonth;
// if calculated > 3
if(monToExp > 3){
res.append(defaultTillExpMonth);
} else {
res.append(monToExp);
}
output.add(res.toString());
}
}
// Write into the same file.
// First We'll delete everything in the input file and then write the modified records
p = new PrintWriter(new FileWriter("output.txt",false));
// Ouch. Very bad way to handle resources. You should find a better way
p.print("");
p.close();
// Write into file
p = new PrintWriter(new FileWriter("InputFile"));
for(String row : output)
{
p.println(row);
}
} else {
System.out.println("No records to process");
}
} catch(IOException e){
e.printStackTrace();
} finally { // Close file
if(p!=null){
p.close();
}
if(bufferedReader!=null){
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
I would strongly recommend you to understand what file resources are, how to handle them efficiently and improve this code. Later on you should move to Apache Commons Library