# desc, idesc, xdesc¶

Q chooses from a variety of algorithms, depending on the type and data distribution.

## desc¶

Descending sort

desc x    desc[x]

Returns x sorted into descending order. The function is uniform. The sort is stable: it preserves order between equals.

Where x is a

• vector, it is returned sorted
• mixed list, the result is sorted within datatype
• dictionary, returns it sorted by the values
• table, returns it sorted by the first non-key column and with the sorted attribute set on that column

Unlike asc, which sets the parted attribute where there are other non-key columns, desc sets only the sorted attribute.

q)desc 2 1 3 4 2 1 2                    / vector
4 3 2 2 2 1 1

q)desc (1;1b;"b";2009.01.01;"a";0)      / mixed list
2009.01.01
"b"
"a"
1
0

q)desc abc!2 1 3                     / dictionary
c| 3
a| 2
b| 1

q)desc([]a:3 4 1;b:ads)              / table
a b
---
4 d
3 a
1 s
q)meta desc([]a:3 4 1;b:ads)
c| t f a
-| -----
a| j
b| s
domain: b g x h i j e f c s p m d z n u v t
range:  b g x h i j e f c s p m d z n u v t

## idesc¶

idesc x    idesc[x]

Where x is a list or dictionary, returns the indices needed to sort list it in descending order.

q)L:2 1 3 4 2 1 2
q)idesc L
3 2 0 4 6 1 5
q)L idesc L
4 3 2 2 2 1 1
q)(desc L)~L idesc L
1b
q)idesc acb!1 2 3
bca
domain: b g x h i j e f c s p m d z n u v t
range:  j j j j j j j j j j j j j j j j j j

## xdesc¶

Sorts a table in descending order of specified columns. The sort is by the first column specified, then by the second column within the first, and so on.

x xdesc y    xdesc[x;y]

Where x is a symbol vector of column names defined in y, which is passed by

• value, returns

y sorted in descending order by x.

The sorted attribute is not set. The sort is stable, i.e. it preserves order amongst equals.

q)\l sp.q
q)s
s | name  status city
--| -------------------
s1| smith 20     london
s2| jones 10     paris
s3| blake 30     paris
s4| clark 20     london
q)city xdesc s                 / sort descending by city
s | name  status city
--| -------------------
s2| jones 10     paris
s3| blake 30     paris
s1| smith 20     london
s4| clark 20     london
q)meta city xdesc s            / s# attribute not set
c     | t f a
------| -----
s     | s
name  | s
status| i
city  | s

Duplicate column names xdesc signals dup if it finds duplicate columns in the right argument. (Since V3.6 2019.02.19.)

### Sorting data on disk¶

xdesc can sort data on disk directly, without loading the entire table into memory: see xasc.

Duplicate keys in a dictionary or duplicate column names in a table will cause sorts and grades to return unpredictable results.