topic Re: Binary Search in Application Development and Automation Discussions

Binary Search

Former Member — Wed, 18 Feb 2009 17:00:33 GMT

Would the following binary search produce correct results?

Internal table IT is sorted by field1 field2 field3

read table IT with key field2 = 'X' field3 = 'Y'

I am not sure this is correct since the read statement makes no

reference to field1.

Re: Binary Search

former_member156446 — Wed, 18 Feb 2009 17:03:44 GMT

use all the fields you used to sort , to read as well

this will:

read table IT with key field1 =  'X' field2 = 'X' field3 = 'Y'

Re: Binary Search

Former Member — Wed, 18 Feb 2009 17:11:57 GMT

Binary search always use divide and conquer method:

So ex:

Field1 Field2 Field3

ZX BC ZA

XY DE YH

ZA AA ZA

After Sort on Field1 Field2 Field3

result will be:

XY DE YH

ZA AA ZA

ZX BC ZA

If we dont use Field on in read the result will not be accurate.

IF you want to use field2 .

USE :

Sort itab by field2 field3.

Read table itab with key field2 field3 BINARY SEARCH.

Hope this resolves your query.

Regards,

Gurpreet

Re: Binary Search

Former Member — Wed, 18 Feb 2009 17:12:43 GMT

It depends on what you mean by "correct". Why not try it and see if you get the results you want?

Rob

Re: Binary Search

Former Member — Wed, 18 Feb 2009 17:26:46 GMT

You could determine the result by running this. You'll see that it returns the first row. It is not, by the way, a binary search. And there is no way to make it binary unless you provide the entire key.

TYPES:  BEGIN OF _ty_1,
        field1(1)  TYPE c,
        field2(1)  TYPE c,
        field3(1)  TYPE c.
TYPES:  END   OF _ty_1.


DATA:
  g_t_tab TYPE TABLE OF _ty_1,
  g_s_line TYPE _ty_1.

g_s_line-field1 = 'A'.
g_s_line-field2 = 'X'.
g_s_line-field3 = 'Y'.
APPEND g_s_line TO g_t_tab.

g_s_line-field1 = 'B'.
g_s_line-field2 = 'X'.
g_s_line-field3 = 'Y'.
APPEND g_s_line TO g_t_tab.

g_s_line-field1 = 'C'.
g_s_line-field2 = 'X'.
g_s_line-field3 = 'Y'.
APPEND g_s_line TO g_t_tab.

SORT g_t_tab BY field1 field2 field3.

READ TABLE g_t_tab WITH KEY field2 = 'X' field3 = 'Y' into g_s_line.

WRITE:/ g_s_line-field1,sy-subrc.

Re: Binary Search

Former Member — Wed, 18 Feb 2009 19:00:59 GMT

Hi,

there is thumb rule when using a BINARY SEARCH.

when ever you are using a Binary Search for a read SORT the table before read with what ever fields you want, and use the same fields in sequence what you used for sorting ,

if you use different keys Binary search Fails but it works sometimes not always...

sort IT by field1 field2 field3

read table IT with key field1 = 'X' field2 = 'X' field3 = 'Y'

if you are using only field2 and field3 as key then sort internal table by field2 and field3 only.

Regards,

vinayaka