sas dataset with index

[HeatherNewton]

Hi if I have created an index for my dataset, does that mean sorting is not required anymore for this dataset prior to merging? As I see this in some programs with index where sort is not added before merge..

[PeterClemmensen]

Yes. Though, all the data sets in the Merge Statement must be either sorted or have an appropriate index.

See the small example below

data one;
input x y1;
datalines;
1 10
3 20
2 30
;

data two;
input x y2;
datalines;
1 40
2 50
3 60
;

proc datasets lib = work nolist;
   modify one;
   index create x;
run;quit;

data want;
   merge one two;
   by x;
run;

[LinusH]

Even if it's technically possible to merge on indexed variables, it's seldom a good idea.

In most situations sorting is much faster.

[Kurt_Bremser · Accepted solution]

I've never used indexes for sorting. Indexes are only good when you need to extract a small (read: 10% or less) subset of the dataset. In all other cases, they only add additional I/O and therefore processing time.