ratios

Ratios between items

ratios y     ratios[y]

Where y is a non-symbolic sortable list, returns the ratios of the underlying values of consecutive pairs of items of y.

ratios is an aggregate function.

Examples: queries to get returns on prices:

update ret:ratios price by sym from trade
select log ratios price from trade

In a query to get price movements:

update diff:deltas price by sym from trade

With signum to count the number of up/down/same ticks:

q)select count i by signum deltas price from trade
price| x
-----| ----
-1   | 247
0    | 3
1    | 252

Implicit iteration

ratios applies to dictionaries and tables.

q)k:`k xkey update k:`abc`def`ghi from t:flip d:`a`b!(10 21 3;4 5 6)

q)ratios d
a| 10  21        3
b| 0.4 0.2380952 2

q)ratios t
a         b
--------------
10        4
2.1       1.25
0.1428571 1.2

q)ratios k
k  | a         b
---| --------------
abc| 10        4
def| 2.1       1.25
ghi| 0.1428571 1.2

First predecessor

The predecessor of the first item is 1.

q)ratios 2000 2005 2007 2012 2020
2000 1.0025 1.000998 1.002491 1.003976

It may be more convenient to have 1 as the first item of the result.

q)ratios0:{first[x]%':x}
q)ratios0 2000 2005 2007 2012 2020
1 1.0025 1.000998 1.002491 1.003976

Subtract Each Divide

The derived function %': (Divide Each Prior) used to define ratios is variadic and can be applied as either a unary or a binary.

However, ratios is supported only as a unary function. For binary application, use the derived function.

---

Each Prior, differ, Divide
Mathematics