6C. Grading
Grading is the assignment of an ordinal number to each item of an array, with all numbers distinct, and with the earliest of equal values being assigned a lower ordinal number. Grading can be used to produce the permutation that will put an array in order. Since sorting is a primitive operation in J, grading is more commonly used to put a companion array into an order derived from another array. For example, a table of addresses may be put into an order derived from a table of last names.
m0=: /: |
Grade y up |
m1=: \: |
Grade y down |
d2=: /:@i. |
Grade y up according to key x |
d3=: \:@i. |
Grade y down according to key x |
{{{ y=:'leap','note',:'file'
- (] ; m0 ; (m0 { ]) ; m1 ; (m1 { ])) y
+
+
+
+
+
+ |leap|2 0 1|file|1 0 2|note| |note| |leap| |leap| |file| |note| |file| +
+
+
+
+
+
- x=: ' abcdefghijklmnopqrstuvwxyz' [ y=: 'senator' x (d2 ; (d2{]) ; d3 ; (d3{])) y
+
+
+
+
+ |3 1 2 5 6 0 4|aenorst|4 0 6 5 2 1 3|tsronea| +
+
+
+
+ }}}