In DBeaver I have a table containing some GPS coordinates stored as Postgis LINESTRING format.
My questions is: If I have, say, this info:
LINESTRING(20 20, 30 30, 40 40, 50 50, 60 60, 70 70)
which built-in ST function can I use to get every N-th element in that LINESTRING? For example, if I choose 2, I would get:
LINESTRING(20 20, 40 40, 60 60)
, if 3:
LINESTRING(20 20, 50 50)
and so on.
I've tried with ST_SIMPLIFY and ST_POINTN, but that's now exactly what I need because I still want it to stay a LINESTRING but just with less points (lower resolution).
Any ideas?
Thanks :-)
Welcome to SO. Have you tried using ST_DumpPoints and applying a module % over the vertices path? e.g. every second record:
WITH j AS (
SELECT
ST_DumpPoints('LINESTRING(20 20, 30 30, 40 40, 50 50, 60 60, 70 70)') AS point
)
SELECT ST_AsText(ST_MakeLine((point).geom)) FROM j
WHERE (point).path[1] % 2 = 0;
st_astext
-------------------------------
LINESTRING(30 30,50 50,70 70)
(1 Zeile)
Further reading:
ST_MakeLine
CTE
ST_Simplify should return a linestring unless the simplification results in an invalid geometry for a lingstring, e.i., less than 2 vertex. If you always want to return a linestring consider ST_SimplifyPreserveTopology . It ensures that at least two vertices are returned in a linestring.
https://postgis.net/docs/ST_SimplifyPreserveTopology.html
Related
I'm trying to get an output for a multi-response table in col%. I can get a % from column total but not from a fixed based. How do I do it? For example
Past week used (Seg A, Seg B, Seg C) =
Olive Oil: 80, 100, 150
Sunflower Oil: 35, 95, 105
Coconut Oil: 109, 209, 15
Segment sizes A=120, B=250, C=165
I need col% by each segment
So Seg A should be calculated as
Olive Oil= 80/120; Sunflower Oil=35/120 & Coconut Oil=109/120
Similarly for Seg B & Seg C.
I'm using tidyr and dplyr to generate my outputs.
Any advice will be much appreciated.
Let's say I have a table storing users, the number of red balls they have, the total number of balls (blue, yellow, other colors etc.), and the ratio of red to total balls.
Schema looks like this:
**user_id** | **ratio** | **red_balls** | **total_balls**
1 .2 2 10
2 .3 6 20
I want to select the 0, 25, 50, 75, and 100 percentile values based on ordering the red_balls column, so this doesn't mean I want the 0, 0.25, etc. values for the ratio column. I want the 25th percentile of the red_balls column. Any suggestions?
I think this can do what you want:
select *
from your_table
where ratio in (0, 0.25, 0.5, 0.75, 1)
order by red_balls
Query finds all rows with ratios that exactly one of 0, 25, 50, 75, 100 and sort rows in ascending order by count of red_balls
I am trying to break down a given number into 10 equal parts and then compare a row of numbers and see in which of the 10 parts they fall under.
ref_number, number_to_check
70, 34
70, 44
70, 14
70, 24
In the above data set, I would like to break 70 into 10 equal parts (in this case it would be 7,14,21, and so on till 70). Next I would like to see in which "part" does the value in column "number_to_check" fall into.
Output expected:
ref_number, number_to_check, part
70, 34, 5
70, 44, 7
70, 14, 2
70, 24, 4
You want arithmetic. If I understand correctly:
select ceiling(number_to_check * 10.0 / ref_number)
Here is a db<>fiddle (the fiddle happens to use Postgres).
In dask or even pandas how would you go about grouping an dask data frame that has a 3 columns of time / level / spread into a set of fixed ranges by time.
Time is only used to move one direction. Like a loop counting up. So the end result would be start time and end time with high of level, low of level, first value of level and last value of level over the fixed range? Example
12:00:00, 10, 1
12:00:01, 11, 1
12:00:02, 12, 1
12:00:03, 11, 1
12:00:04, 9, 1
12:00:05, 6, 1
12:00:06, 10, 1
12:00:07, 14, 1
12:00:08, 11, 1
12:00:09, 7, 1
12:00:10, 13, 1
12:00:11, 8, 1
For a fixed level range of (7). So level from start to end can not be more than 7 total distance from start to end for each bin of level. Just because first bin is only 8 difference in time and second is only 2 different in time, this dose not madder one the high to low madders that the total distance from high to low dose not go passed 7 the fixed bin size. The first bin could have been 5 not 8 for first bin and 200 for next bin not 2 in the example below. So the First few rows in dask would look something like this.
First Time, Last Time, High Level, Low Level, First Level, Last Level, Spread
12:00:00, 12:00:07, 13, 6, 10, 13, 1
12:00:07, 12:00:09, 14, 7, 13, 7, 1
12:00:09, X, 13, 7, X, X, X
How could this be aggregated in dask with a fix window of level moving forward in time binning each time level moves above X or equal too high/low with in X or below X?
I would like to know if there is a function or some sort of way to round a number to lowest whole value. Something like floor, but to a specified increment like 10. So for example:
0.766,5.0883, 9, 9.9999 would all be floored to 0
11.84848, 15.84763, 19.999 would all be floored to 10
etc...
I'm basically looking to fit numbers in the ranges of 0, 10, 20, 30, etc
Can I also do it with different ranges? For example 0, 100, 200, 300, etc
Thank you.
You can do this with arithmetic and floor():
select 10*floor(val / 10)
You can replace the 10s with whatever value you want.