topic Re: How to get previous row (tuple)'s value without using Custom Code components? in Talend Studio

How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Fri, 25 May 2018 12:30:58 GMT

I want to use the previous tuple(s)' value in an expression in tMap.

For eg.,

Input:

A | 2

B | 1

C | 4

D | 1

E | 3

Output (previous 2 tuples added):

A | 2 | 2

B | 1 | 3

C | 4 | 7

D | 1 | 6

E | 3 | 8

How to extract it in tMap expression? Or is there any other component to do it? I do not want to use stuff like tJavaXXXX or tPerlXXXX etc Custom Code or Database query components, which are shortcuts.

Re: How to get previous row (tuple)'s value without using Custom Code components?

manodwhb — Mon, 28 May 2018 06:06:27 GMT

@TalendSpree,are you looking for the below one?

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 28 May 2018 07:26:16 GMT

@manodwhb This is an accumulation of all previous values. What I'm looking for is a cumulative sum of previous 'n' values. Thanks for taking the time to implement my problem, though!

Re: How to get previous row (tuple)'s value without using Custom Code components?

SachinD — Mon, 28 May 2018 14:08:05 GMT

Hi @TalendSpree

I achieved this using tMemorize and tJavaFlex but as you have mentioned you want the solution without using tJavaFlex code.

Sachin D

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Wed, 30 May 2018 06:12:45 GMT

@SachinD Thanks for taking the time to implement my problem! I would actually like to know how you're using `tMemorizeRows` and it's output in `tJavaFlex`.

Re: How to get previous row (tuple)'s value without using Custom Code components?

SachinD — Wed, 30 May 2018 09:09:22 GMT

Thanks @TalendSpree

Please check below screenshots.

I quickly tried it, if you need you can change little code in tJavaFlex if required.

Thanks,

click Accept the solution if it helps
and
kudos are welcome when a reply is helpful.

Sachin D

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Wed, 30 May 2018 09:30:45 GMT

To do this in a tMap you can use the tMap variables. These are more powerful than they look because of two key features; they keep their values between rows and they are processed from top to bottom in order. As such you can configure them to hold the last value of individual columns and compare them against the current value.

Below is an example of how this can be done......

Notice the order in which the variables are assigned and how the _last variables (representing the last row) are set by the _this variables (which are actually set by the current row) before those variables are set by the current row.

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Thu, 31 May 2018 06:55:22 GMT

Thanks @SachinD ... can we use `globalMap("tMemRows")` in `tMap` component? I've tried, but I get the following error.

Exception in component tMap_1 (tMemRows)
java.lang.NullPointerException
at local_project.tmemrows_0_1.tMemRows.tFileInputDelimited_1Process(tMemRows.java:1126)
at local_project.tmemrows_0_1.tMemRows.runJobInTOS(tMemRows.java:1669)
at local_project.tmemrows_0_1.tMemRows.main(tMemRows.java:1518)

@rhall Thank you for the help! This is closest to what I was looking for. Only issue is, if I want to change the number of accumulations, I'll have to do it manually. Any suggestions?

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Thu, 31 May 2018 11:18:28 GMT

What do you mean by the number of accumulations? Do you mean the number of held rows or the number of columns to hold? You can achieve increases in both, but you are right that you will have to do it manually. This is where you have to decide which is the best approach to take; to use other components (like the memorize rows component) and a bit of Java or keep it all in the tMap. This is why I like Talend because you have this choice 🙂

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Thu, 31 May 2018 13:51:23 GMT

Thanks @rhall ! I meant increase the number of rows.

Do you have any other tips & tricks on Talend components?

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Thu, 31 May 2018 14:20:21 GMT

There are a few, but I don't tend to think about them as "tricks", just how I use them to solve certain problems. Nothing that I can just "list" I'm afraid 🙂

Re: How to get previous row (tuple)'s value without using Custom Code components?

SachinD — Thu, 31 May 2018 14:50:10 GMT

Thanks @rhall

I too tried your solution, and it works perfectly fine.

I tried such thing with tMap for first time and now understood power of tMap.

Thanks for sharing such solution, please keep sharing such good tricks.

Also Thanks @TalendSpree for posting this topic.

Sachin D.

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 19 Nov 2018 07:21:26 GMT

Hi, can you share the configuration of the tmap please??

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 19 Nov 2018 07:46:27 GMT

Hello, can you share the TMap editor . Thank you

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 19 Nov 2018 09:38:24 GMT

There is a screenshot above that shows the configuration. Click on it and it will allow you to zoom in.

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 19 Nov 2018 10:37:05 GMT

how to i access the next row elements? is there any method where instead of previous row i want the next row . thnk you in advance

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Mon, 19 Nov 2018 11:01:03 GMT

No, you can't do that. But what is wrong with this method? You are essentially accessing the "next" row, just not in the way you think it should work. The other way this could be done is to simply use a sorting component to reverse the rows, then reverse then back after the component you wish to carry out your logic in.

Re: How to get previous row (tuple)'s value without using Custom Code components?

Slope — Wed, 11 Mar 2020 14:33:36 GMT

Hello,

Thanks @rhall your solution help me a lot but my need is a bit different.

Here's what I've with the current solution :

OUTPUT 1 :

A | 2 | 2

B | 1 | 3

C | 4 | 7

D | 1 | 6

But what I need is :

A | 2 | 2

A | 1 | 3

B | 1 | 1

C | 1 | 1

C | 3 | 4

So I would like to "reset" the count for each different kind of input (A, B, C).

Re: How to get previous row (tuple)'s value without using Custom Code components?

Anonymous — Wed, 11 Mar 2020 20:31:52 GMT

Hi @Slope,

This looks like it might be a slightly different problem. Can you raise this in a new thread and completely explain the problem please?

Thanks

Re: How to get previous row (tuple)'s value without using Custom Code components?

Slope — Fri, 13 Mar 2020 06:55:40 GMT

Hi,

I created a new post before replying on this one.

Here's the link : https://community.talend.com/t5/Design-and-Development/Aggregation-on-one-attribut-and-keeping-date/m-p/215426#M118465

Kind regards