从q中删除表中的列

Question

我试图从表中删除一个列而不丢失数据,因此可以再次恢复数据,但是当q表进程加载时,删除的列将不会显示.显然我的代码不起作用.有没有特定的q可以做到这一点？dir是表的位置,c是要删除的列.

{[dir;t;c] delete c from (` sv (dir,t),`)}

Answer 1

kdb +有一种简单的方法来"删除"一列而不实际删除列数据.如果查看存储表的目录,则应该能够识别.d文件.这是kdb +存储表列的正确顺序的位置.要删除列,只需从该.d文件中删除列名称即可.例如:

q)get `:test/.d
`sym`time`src`bid`ask`bsize`asize
q)
q)`:test/.d set `sym`time`src`bid`ask`bsize
`:test/.d
q)
q)test
sym  time                          src bid   ask   bsize asize
--------------------------------------------------------------
AAPL 2014.04.21D08:00:00.456000000 L   25.32 25.36 8000  8500
AAPL 2014.04.21D08:00:01.387000000 O   25.32 25.35 9500  2500
AAPL 2014.04.21D08:00:10.348000000 N   25.35 25.35 8000  5000
AAPL 2014.04.21D08:00:10.532000000 L   25.33 25.37 5000  7000
AAPL 2014.04.21D08:00:15.163000000 L   25.34 25.36 10000 8000
AAPL 2014.04.21D08:00:15.847000000 N   25.32 25.36 1500  500
AAPL 2014.04.21D08:00:16.335000000 N   25.33 25.34 8500  5500
AAPL 2014.04.21D08:00:17.017000000 N   25.33 25.34 9000  2500
AAPL 2014.04.21D08:00:17.634000000 N   25.3  25.36 9500  1000
AAPL 2014.04.21D08:00:19.427000000 L   25.33 25.36 9500  5000
AAPL 2014.04.21D08:00:24.629000000 N   25.33 25.37 6000  2000
AAPL 2014.04.21D08:00:25.207000000 L   25.33 25.36 5000  2500
AAPL 2014.04.21D08:00:29.962000000 L   25.32 25.38 3500  5000
AAPL 2014.04.21D08:00:31.998000000 O   25.34 25.36 5500  4000
AAPL 2014.04.21D08:00:33.795000000 N   25.34 25.36 5000  3500
AAPL 2014.04.21D08:00:34.651000000 L   25.35 25.37 7500  6500
AAPL 2014.04.21D08:00:38.843000000 O   25.33 25.36 4000  6500
AAPL 2014.04.21D08:00:40.062000000 L   25.33 25.38 2000  9500
AAPL 2014.04.21D08:00:43.508000000 N   25.35 25.36 6500  10000
AAPL 2014.04.21D08:00:46.823000000 N   25.35 25.38 6000  7500
..
q)\l .
q)test
sym  time                          src bid   ask   bsize
--------------------------------------------------------
AAPL 2014.04.21D08:00:00.456000000 L   25.32 25.36 8000
AAPL 2014.04.21D08:00:01.387000000 O   25.32 25.35 9500
AAPL 2014.04.21D08:00:10.348000000 N   25.35 25.35 8000
AAPL 2014.04.21D08:00:10.532000000 L   25.33 25.37 5000
AAPL 2014.04.21D08:00:15.163000000 L   25.34 25.36 10000
AAPL 2014.04.21D08:00:15.847000000 N   25.32 25.36 1500
AAPL 2014.04.21D08:00:16.335000000 N   25.33 25.34 8500
AAPL 2014.04.21D08:00:17.017000000 N   25.33 25.34 9000

删除后,kdb +不会将列与您的表关联,并且在调用内存时不会显示该列.

希望这可以帮助.