>From Insert in Dictionary:
If y has no items (that is, 0=#y), the result of u/y is the
neutral or identity element of the function u.
Basic Characteristics (b.) gives the identity functions
b=. 3 : '".y,'' b. 1'''
(,. b&.>) +`*`+.`*.`>.`<.
+--+----------+
|+ |0 $~ [EMAIL PROTECTED] |
+--+----------+
|* |1 $~ [EMAIL PROTECTED] |
+--+----------+
|+.|0 $~ [EMAIL PROTECTED] |
+--+----------+
|*.|1 $~ [EMAIL PROTECTED] |
+--+----------+
|>.|__ $~ [EMAIL PROTECTED]|
+--+----------+
|<.|_ $~ [EMAIL PROTECTED] |
+--+----------+
+/0 2 3$0
0 0 0
0 0 0
>./0 2 3$0
__ __ __
__ __ __
If you were to implement Insert, it would use
the identity element as initializer:
ins=: 1 : 0
".'id=.',u b. 1
r=. id y
for_i. |.y do. r=. i u r end.
)
+ ins 1 2 3
6
+ ins ''
0
+ ins i.3 4
12 15 18 21
+/ i.3 4
12 15 18 21
+ ins 3 4$0
0 0 0 0
+/ 3 4$0
0 0 0 0
----- Original Message ----
From: Anssi Seppälä <[EMAIL PROTECTED]>
To: Programming forum <[email protected]>
Sent: Sunday, July 9, 2006 12:23:00 PM
Subject: [Jprogramming] Sum of empty vector
Working with practical statistics and samples that can be also empty
I find that J follows a kind of logic that is uncomfortable. Taking
a empty vector 0$0 (empty sample) :
+/0$0 NB. sum of empty sample is zero !
0
(+/ % #) 0$0 NB. mean of empty sample is also zero !
0
I wonder why (+/0$0) could not be 0$0 instead of 0 ?
Anssi
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