Skip to content

get, set

Read or set the value of a variable or a kdb+ data file


Read or memory-map a variable or kdb+ data file

Syntax: get x, get[x]

Reads or memory maps kdb+ data file x. A type error is signalled if the file is not a kdb+ data file.

Used to map columns of databases in and out of memory when querying splayed databases, and can be used to read q log files, etc.

q)get `a

q)\l trade.q
q)`:NewTrade set trade                  / save trade data to file
q)t:get`:NewTrade                       / t is a copy of the table
q)`:SNewTrade/ set .Q.en[`:.;trade]     / save splayed table
q)s:get`:SNewTrade/                     / s has columns mapped on demand

get and value

get has several other uses. The function value is a synonym for get. By convention, it is used for other purposes. But the two are completely interchangeable.

q)value "2+3"
q)get "2+3"


Assign a value to a variable or file

Syntax: x set y, set[x;y]

Where x is

assigns the value of y to variable name or filename x.

q)`a set 1 2 3            / set name a
1 2 3

q)a set 1 2 3             / set name t (indirect assignment)
1 2 3

q)a set 1 2 3             / fails, as name must be a symbol

If x is a file symbol, the values are written to file.

q)`:work.dat set 1 2 3    / write values to file
q)get `:work.dat
1 2 3

Write a table to a single file:

q)\l sp.q
q)`:mytable.dat set sp
q)get `:mytable.dat
s  p  qty
s1 p1 300
s1 p2 200
s1 p3 400

To save a table splayed across a directory, x must be a path (i.e. ends with a /), and the table must be fully enumerated, with no primary keys:

q)`:mydata/ set sp
q)\ls mydata
q)get `:mydata
s  p  qty
s1 p1 300
s1 p2 200
s1 p3 400

set saves the data in a binary format akin to tag+value, retaining the structure of the data in addition to its value.

q)`:data/foo set 10 20 30
q)read0 `:data/foo
"\376 \007\000\000\000\000\000\003\000\000\000\000\000\000\000"

Avoid Kx namespaces

Avoid setting variables in the Kx namespaces, as undesired and confusing behavior can result.

These are .h, .j, .Q, .q, .z, and any other namespaces with single-character names.

File system