Re: frequency of positive and negative numbers, sizes of numbers and frequency of alteration of polarity

On Fri, Feb 18, 2022 at 9:11 AM Shaozhong SHI <shishaozhong(at)gmail(dot)com> wrote:
> How to calculate frequency of positive and negative numbers and define and calculate frequency of alteration of polarity?
>
> Surely, we can use frequency of alteration of polarity and level of change (e.g., size of positive and negative numbers) to measure degree and frequency of alteration.
>
> Any ideas in doing so in postgres tables' columns full of positive and negative numbers?

Window functions might be useful to detect polarity changes:

postgres=# create table time_series (time int, value int);
CREATE TABLE
postgres=# insert into time_series values (1, -5), (2, -5), (3, 10), (4, -3);
INSERT 0 4
postgres=# select time,
value,
sign(lag(value) over (order by time)) != sign(value)
as flipped
from time_series;
time | value | flipped
------+-------+---------
1 | -5 |
2 | -5 | f
3 | 10 | t
4 | -3 | t
(4 rows)