Use macro logic to determine the nth root of a value even if the value is negative.

The macro has three parameters:

  INVAR contains the value whose nth root is to be determined
  OUTVAR contains the nth root = INVAR**(1/ROOT)
  ROOT contains the root to take.

For example, if you want to take the cube root, set ROOT equal to 3.

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These sample files and code examples are provided by SAS Institute Inc. "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Recipients acknowledge and agree that SAS Institute shall not be liable for any damages whatsoever arising out of their use of this material. In addition, SAS Institute will provide no support for the materials contained herein.

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%macro nroot(invar,outvar,root);

  /* If the root is odd, then take the root of the absolute value and */
  /* multiply by the sign of the original value                       */
  if mod(&root,2)=1 then &outvar=sign(&invar)*abs(&invar)**(1/&root);
  else do;

    /* If the root is even and the original value is negative then */
    /* assign a missing value                                      */
    if &invar<0 then &outvar=.;

    /* Otherwise just take the root */
    else &outvar=&invar**(1/&root);
  end;
%mend nroot;



/* Use the macro */

data test;

  /* Generate some data */
  do i=1 to 10;
    x=rannor(123);
    y=x**3;

    /* Take the square root of y and store in y2root */
    %nroot(y,y2root,2);

    /* Take the cube root of y and store in y3root */
    %nroot(y,y3root,3);
    output;
  end;
run;

proc print data=test;
run;

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These sample files and code examples are provided by SAS Institute Inc. "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Recipients acknowledge and agree that SAS Institute shall not be liable for any damages whatsoever arising out of their use of this material. In addition, SAS Institute will provide no support for the materials contained herein.

    Obs     i        x           y        y2root     y3root

      1     1    -0.32659    -0.03484     .         -0.32659
      2     2     1.54244     3.66963    1.91563     1.54244
      3     3     0.25903     0.01738    0.13183     0.25903
      4     4    -0.55583    -0.17173     .         -0.55583
      5     5     0.77872     0.47222    0.68718     0.77872
      6     6    -0.65520    -0.28127     .         -0.65520
      7     7    -0.02210    -0.00001     .         -0.02210
      8     8    -0.77265    -0.46126     .         -0.77265
      9     9     0.72423     0.37987    0.61634     0.72423
     10    10     1.26331     2.01620    1.41993     1.26331

Use macro logic to determine the nth root of a value even if the value is negative.

Type:	Sample
Topic:	SAS Reference ==> DATA Step SAS Reference ==> Functions ==> Mathematical

Date Modified:	2005-12-16 03:02:54
Date Created:	2004-09-30 14:08:58

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