If you want to "look ahead" you simply adjust this slightly to hold processing the first row until the second has arrived. Thus allowing you to appear to "look ahead"
It is not possible for the current row to get the "next" as such. So what I am suggesting is using a variation on what that tutorial shows.
When your job reads the first row, it is essentially stored in memory. Then, when the second row arrives, the first row does what it needs to with the second row's data, is released and then the second row is stored in memory. This goes on throughout the job until you get to the end of the data set.
This is enabled by the fact that the tMap variables are processed from top to bottom and are held between data rows. Using this functionality (as described in the tutorial....you can literally follow it and recreate it in an example job to see it happening), you can do this inter-row calculation.
In my scenario , current row's data will be modified as per next row's data .So as per your suggestion if i store the first row data in a variable and wait for the second row to arrive , i can compare that with the variable value but how can i edit the previous row data based on this comparison ?
The previous row's data is in memory. You can edit it in memory as well.
When you output the variables that the row columns are stored in, you can modify the data there....or do it in another tMap variable.
This isn't *easy*, but it is possible and quite logical when you get your head into it. Try it out. The best way to learn something like this is to test it in an example job.
I referred the link you have provided but getting error.
My requirement is to store previous record hashkey and price value in two variables. if hashkey is same calculate price difference as below
input
hash key | postcode | Price
1000 abc 100,000
1000 abc 200,000
1000 abc 250,000
1001xyz 50,000
1001xyz 250,000
expected:
hash key | postcode | Price| profitmade
1000| abc |100,000|0
1000| abc | 200,000 |100,000
1000| abc|250,000 |50,000
1001 | xyz |50,000 | 0
1001 | xyz| 250,000 | 200,000
Error I am getting:
org.talend.designer.runprocess.ProcessorException: Job compile errors At least job "testfile" has a compile errors, please fix and export again. Error Line: 1275 Detail Message: v_Prev_Price cannot be resolved to a variable
OK, when using tMap variables, they are referred to using Var. before the name. So your variables should be named like this Var.v_Prev_Price, for example. You can drag and drop your tMap variables to another tMap variable expression if you like. That should show you how the names should be formatted. This is almost certainly the cause of your Java error.
In my opinion, the simplest is to use a tJavaRow instead of a tMap for this case.
It should look like this:
// Initialize output_row fields from input_row fields values
output_row.hashkey = input_row.hashkey;
output_row.postcode = input_row.postcode;
output_row.price = input_row.price;
// Set ProfitMade depending on comparison result of previous and current hashkey
if((Integer)globalMap.get("PrevHash") != null && (Integer)globalMap.get("PrevHash") == input_row.hashkey)
output_row.ProfitMade = input_row.Price - (Integer)globalMap.get("PrevPrice");
else
output_row.ProfitMade = 0;
// Set the global variables values for next iteration
globalMap.set("PrevHash", input_row.hashkey);
globalMap.set("PrevPrice", input_row.Price);
Check field names and datatypes (integer vs float) before to try this in your job.
Thank rhall, I added 'Var' before using variable and it worked. but facing datatype incompatible issue now.
hashkey field data is being generated using MD5 function(which is basically hexadecimal). My source is file. talend reading hashkey as string and giving below error datatype defined in talend is int ( I tried changing datatype as int, long etc)
[statistics] connecting to socket on port 3446
[statistics] connected
For input string: "hashkey"
For input string: "ddbfcac5d5bb83f97906b3326e4dfd97"
For input string: "ddbfcac5d5bb83f97906b3326e4dfd97"
For input string: "ddbfcac5d5bb83f97906b3326e4dfd97"
For input string: "ddbfcac5d5bb83f97906b3326e4dfd97"
For input string: "ddbfcac5d5bb83f97906b3326e4dfd97"
[statistics] disconnected
Job testfile ended at 14:17 01/11/2017. [exit code=0]
