Find the mode in BigQuery - google-bigquery

Question

The mode is the value that appears most often in a set.
I would like something like:
SELECT
t.id as t_id,
GROUP_CONCAT(t.value) as value_list,
MODE(t.value) AS value_mode
FROM dataset.table as t
GROUP BY t_id
such that, for example:
t_id value_list value_mode
1 2,2,2,3,6,6 2
How is that done?
EDIT: The value_list is just there for illustration purpose. Only need the mode

Answer 1

select id, value as value_list, v as value_mode
from (
select
id, value, v,
count(1) as c,
row_number() over(partition by id order by c desc) as top
from (
select id, value, split(value) as v
from dataset.table
)
group by id, value, v
)
where top = 1

Answer 2

I often have to find the mode of prices for respective groups (e.g. length and amps) to filter out sale prices and the like.
I typically use two methods both with creating an array and un-nesting it in order of frequency. One method I use is by a LIMIT another with an [OFFSET(0)] in case you want to get Nth values.
Both are included below:
WITH t AS (SELECT 18 AS length,
'HIGH' as amps,
99.95 price UNION ALL
SELECT 18, "HIGH", 99.95 UNION ALL
SELECT 18, "HIGH", 5.95 UNION ALL
SELECT 18, "LOW", 33.95 UNION ALL
SELECT 18, "LOW", 33.95 UNION ALL
SELECT 18, "LOW", 4.5 UNION ALL
SELECT 3, "HIGH", 77.95 UNION ALL
SELECT 3, "HIGH", 77.95 UNION ALL
SELECT 3, "HIGH", 9.99 UNION ALL
SELECT 3, "LOW", 44.95 UNION ALL
SELECT 3, "LOW", 44.95 UNION ALL
SELECT 3, "LOW", 5.65
)
SELECT
length,
amps,
-- By Limit
(SELECT x FROM UNNEST(price_array) x
GROUP BY x ORDER BY COUNT(*) DESC LIMIT 1 ) most_freq_price,
(SELECT x FROM UNNEST(price_array) x
GROUP BY x ORDER BY COUNT(*) ASC LIMIT 1 ) least_freq_price,
-- By Offset
ARRAY((SELECT x FROM UNNEST(price_array) x
GROUP BY x ORDER BY COUNT(*) DESC))[OFFSET(0)] most_freq_price_offset,
ARRAY((SELECT x FROM UNNEST(price_array) x
GROUP BY x ORDER BY COUNT(*) ASC))[OFFSET(0)] least_freq_price_offset
FROM (
SELECT
length,
amps,
ARRAY_AGG(price) price_array
FROM t
GROUP BY 1,2
)

Answer 3

For your example, this is how I would solve it:
SELECT x, w mode
FROM (
SELECT COUNT(*) c, w, ROW_NUMBER() OVER(ORDER BY c DESC) rn, FIRST(x) x
FROM (
SELECT SPLIT(x) w, x FROM (SELECT "2,2,2,3,6,6" x)
)
GROUP BY 2
)
WHERE rn=1
And with the GROUP_CONCAT within query:
SELECT gc, w mode
FROM (
SELECT COUNT(*) c, w, ROW_NUMBER() OVER(ORDER BY c DESC) rn, FIRST(gc) gc
FROM (
SELECT GROUP_CONCAT(w) OVER() gc, w
FROM (FLATTEN((
SELECT SPLIT(x) w, x FROM (SELECT "2,2,2,3,6,6" x)), w)
)
)
GROUP BY 2
)
WHERE rn=1
And handling partitions:
SELECT tid, gc value_list, w value_mode
FROM (
SELECT tid, COUNT(*) c, w, ROW_NUMBER() OVER(PARTITION BY tid ORDER BY c DESC) rn, FIRST(gc) gc
FROM (
SELECT tid, GROUP_CONCAT(w) OVER(PARTITION BY tid) gc, w
FROM (FLATTEN((
SELECT 1 tid, SPLIT(x) w, x FROM (SELECT "2,2,2,3,6,6" x)), w)
)
)
GROUP BY tid, w
)
WHERE rn=1

Answer 4

There is a direct function available now
approx_top_count()
Here is an example of its usage
https://cloud.google.com/bigquery/docs/reference/standard-sql/approximate_aggregate_functions#approx_top_count