Regex for Parsing vertical CSV in Athena - regex

Question

So, I've been trying to load csvs from a s3 bucket into Athena. However, the way the csv are designer looks like the following
ns=2;s=A_EREG.A_EREG.A_PHASE_PRESSURE,102.19468,12/12/19 00:00:01.2144275 GMT
ns=2;s=A_EREG.A_EREG.A_PHASE_REF_SIGNAL_TO_VALVE,50.0,12/12/19 00:00:01.2144275 GMT
ns=2;s=A_EREG.A_EREG.A_PHASE_SEC_CURRENT,15.919731,12/12/19 00:00:01.2144275 GMT
ns=2;s=A_EREG.A_EREG.A_PHASE_SEC_VOLTAGE,0.22070877,12/12/19 00:00:01.2144275 GMT
ns=2;s=A_EREG.A_EREG.ACTIVE_PWR,0.0,12/12/19 00:00:01.2144275 GMT
The csv is just one record. Each column of the record has a value associated to it, which sits between two commas between the timestamp and the name, which I am trying to capture.
I've been trying to parse it using Regex Serde and I got to this Regular expression:
((?<=\,).*?(?=\,))
demo
I want the output of the above to be:
col_a col_b col_c col_d col_e
102.19468 50.0 15.919731 0.22070877 0.0
My DDL query looks like this:
CREATE EXTERNAL TABLE IF NOT EXISTS
(...)
ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.RegexSerDe'
WITH SERDEPROPERTIES (
'serialization.format' = '1',
'input.regex' = "\(?<=\,).*?(?=\,)"
) LOCATION 's3://jackson-nifi-plc-data-1/2019-12-12/'
TBLPROPERTIES ('has_encrypted_data'='false');
The table creation Query above works succesfully, but when I try to preview my table I get the following error:
HIVE_CURSOR_ERROR: Number of matching groups doesn't match the number of columns
I am fairly new to Hive and Regex so I don't know what is going on. Can someone help me out here?
Thanks in advance,
BR

Answer 1

One column in Hive table corresponds to one capturing group in the regex. If you want to select single column containing everything between commas then this will work:
'.*,(.*),.*'

Answer 2

Athena serdes require that each record in the input is a single line. Multiline records are not supported.
What you can do instead is to create a table which maps each line in your data to a row in a table, and use a view to pivot the rows that belong together into a single row.
I'm going to assume that the ns field at the start of the lines is an ID, if not, I assume there is some other thing identifying which lines belong together that you can use.
I used your demo to create a regex that matched all the fields of each line and came up with ns=(\d);s=([^,]+),([^,]+),(.+) (see https://regex101.com/r/HnjnxK/5).
CREATE EXTERNAL TABLE my_data (
ns string,
s string,
v double,
dt string
)
ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.RegexSerDe'
WITH SERDEPROPERTIES (
'serialization.format' = '1',
'input.regex' = "ns=(\\d);s=([^,]+),([^,]+),(.+)"
)
LOCATION 's3://jackson-nifi-plc-data-1/2019-12-12/'
TBLPROPERTIES ('has_encrypted_data'='false')
Apologies if the regex isn't correctly escaped, I'm just typing this into Stack Overflow.
This table has four columns, corresponding to the four fields in each line. I've named then ns and s from the data, and v for the numerical value, and dt for the date. The date needs to be typed as a string since it's not in a format Athena natively understands.
Assuming that ns is a record identifier you can then create a view that pivots rows with different values for s to columns. You have to do this the way you want it to, the following is of course just a demonstration:
CREATE VIEW my_pivoted_data AS
WITH data_aggregated_by_ns AS (
SELECT
ns,
map_agg(array_agg(s), array_agg(v)) AS s_and_v
FROM my_data
GROUP BY ns
)
SELECT
ns,
element_at(s_and_v, 'A_EREG.A_EREG.A_PHASE_PRESSURE') AS phase_pressure,
element_at(s_and_v, 'A_EREG.A_EREG.A_PHASE_REF_SIGNAL_TO_VALVE') AS phase_ref_signal_to_valve,
element_at(s_and_v, 'A_EREG.A_EREG.A_PHASE_SEC_CURRENT') AS phase_sec_current,
element_at(s_and_v, 'A_EREG.A_EREG.A_PHASE_SEC_VOLTAGE') AS phase_sec_voltage,
element_at(s_and_v, 'A_EREG.A_EREG.ACTIVE_PWR') AS active_pwr
FROM data_aggregated_by_ns
Apologies if there are syntax errors in the SQL above.
What this does is that it creates a view (but start by trying it out as a query using everything from WITH and onwards), which has two parts to it.
The first part, the first SELECT results in rows that aggregate all the s and v values for each value of ns into a map. Try to run this query by itself to see how the result looks.
The second part, the second SELECT uses the results of the first part and just picks out the different v values for a number of values of s that I chose from your question using the aggregated map.