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How to parse w/ fixed width instead of char delimited contents?

Explorer

I am trying to parse data from file contents that are generated by fixed width instead of by a delimiter. As a simplified example, the value for data attribute 1 is in position 1-2, for attribute 2 is in position 3-6, and attribute 3 is in position 7-8 in each line. Then, the file contents should be transformed as below.

Before

AABBBBCC

DDEEEEFF

After

AA;BBBB;CC

DD;EEEE;FF

I assume there may be a way to capture substrings per line? Please assist.

1 ACCEPTED SOLUTION

Rising Star

Kausha,

You can use ReplaceText to do this. In your example above, you can use a Replacement Strategy of "Regex Replace".

Set Evaluation Mode to "Line-by-Line"

The Search Value would then be:

(.{2})(.{4})(.{2})

And the Replacement Value would be:

$1;$2;$3

Does that help?

View solution in original post

17 REPLIES 17

Rising Star

Kausha,

You can use ReplaceText to do this. In your example above, you can use a Replacement Strategy of "Regex Replace".

Set Evaluation Mode to "Line-by-Line"

The Search Value would then be:

(.{2})(.{4})(.{2})

And the Replacement Value would be:

$1;$2;$3

Does that help?

Explorer

Yes. This works well, but is there a way to store the values as attributes. Ultimately, I want to use the AttributesToJSON processor.

Rising Star

You can use the ExtractText processor and provide it a regex also in order to pull the values into attributes. For example, you could have:

field1: (.{2}).{6}

field2: .{2}(.{4}).{2}

field3: .{6}(.{2})

This assumes, though, that each FlowFile has only a single line. You could use SplitText, for example, to split each FlowFile into a separate line perhaps? I think we may need more context about what you're trying to accomplish to provide a more detailed answer.

Explorer

I have assumed the following flow: GetFile --> ExtractText --> SplitText --> UpdateAttribute --> AttributesToJSON --> PutFile

I receive an error in PutFile. Below are my modified configurations

ExtractText - Enable Multiline Mode = True

SplitText - Line Split Count = 1; Header Line Count = 1

Update Attribute - Properties as suggested Att1 = (.{2}).{6}; Att2 = .{2}(.{4}).{2}; Att3 = .{6}(.{2})

AttributesToJSON Attributes List = Att1, Att2, Att3

What am I missing here?

Rising Star

What error do you see in PutFile?

Explorer

I am able to run the flow when I set the ExtractText-->Splittext connection for matched and unmatched, but with incorrect output: {"Att3":" .{6}(.{2})","Att2":".{2}(.{4}).{2}","Att1":"(.{2}).{6}"}.

Would it be more efficient to use the ReplaceTextWithMapping processor? I am unable to find a template with this processor and a relevant mapping file.

New Contributor

Hi,

I am not able to replicate same example. I am getting output as $1;$2;$3 all the times. I am new to NiFi and I and not able to find where I am missing. I think I have not used Properties correctly.

This is a bit tricky and will require a bit of regex magic. You will want to capture each length of data attribute (2, 4 and 2 respectively) into capture groups then use those capture groups to replace the content.

You'll use the ReplaceText processor with a search value of "(.{2})(.{4})(.{2})" and a replacement value of "$1;$2;$3" and configure it to evaluate line by line. This will go through the contents of the flowfile line by line and replace the contents like you want.

Comment below if you run into any problems!

Explorer

I have posted to @mpayne also: "Yes. This works well, but is there a way to store the values as attributes?" Ultimately, I want to use the AttributesToJSON processor.

Ah so you also want to extract the text to be attributes of the flowfile. Is the structure of the contents only ever two lines and do you want to create JSON using both of those lines or split them into separate flowfiles?

Explorer

The number of rows for the flow files will vary. Each line of data will represent a record/item. Also, I want the data output in its original file, not in separate flowfiles.

What's your end goal JSON schema look like? What identifiers are each of the values going to use (for every line)? As a note, AttributesToJSON only creates flat JSON objects (no nested fields).

Explorer

The output, based on this example would be JSON array

[{"field1":"AA","field2":"BBBB","field3":"CC"},{"field1":"DD","field2":"EEEE","field3":"FF"}]

Assuming you are okay with using Hive for this, you would just create a table with one column (column name something like row) and then load the whole file into that table. Run a query to then split the columns and insert in another table.

Here are more details and code snippet. https://martin.atlassian.net/wiki/pages/viewpage.action?pageId=21299205

didnt realize the question was about nifi.. my bad.

Guru

I agree with @jpercivall and @mpayne ReplaceText is the best way to go. I created a quick workflow that you can reference. This was assuming the input of AABBBBCC as you suggested. You can change the GetFile path and PutFile path, and the regex in ReplaceText to test with your real data.fixedwidthexample.xml

Explorer

I have attempted, unsuccessfully, using the ReplaceText processor. The method works if I have a small/set number of lines in my file.

Do you have any guidance on the ReplaceTextWithMapping processor and how the mapping file should be formatted?

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