Introduction
Python, a common programming language, supports negative indexing for arrays. B4P applies negative indexing on a broader range. Typically, the -1 refers to the last element, with -2, -3, etc. referring to the elements further up (or leftward). At present, negative indexing is used in the following:
- Arrays (-1 = last element)
- Table row numbers (-1 = last row)
- Table column number (-1 = last column. Few exceptions exists where -1 refers to a vacant column after the last one, and is documented so if it applies)
- Set elements (-1 = last set element)
- Function parameters (in selected functions where documented)
Negative numbers must be at least big enough in order to access the first element / row / column. Going further will result in exceptions (error messages).
Programming example
array( a[], { ha, he, hi, ho, hu } );
structure( b[], { reptile, mammal, bird, fish }, { turtle, deer, swallow, dorade } );
c[] = { Hah, Heh, Hih, Hoh, Huh };
echo( a[-2], " ", a[-1] ); // ho, hu
echo( b[-2], " ", b[-1] ); // deer, turtle (last two acc. to alphabetic order of structure members)
echo( c[]{-2}, " ", c[]{-1} ); // Hoh, Huh
echo(new line, "Example with tables:");
table initialize( t, { { Last Name, First Name, Street, City, Country },
{ Adams, Abel, Main St, S. Francisco, USA }, { Billson, Bill, South St, London, UK } } );
echo( [t:-2,-1] ); // Last row, 2nd last column. It's 'London'.
echo( [t:-1,-1] ); // Last row, last column. It's 'UK'. Outcome
ho hu
deer turtle
Hoh Huh
Example with tables:
London
UK