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50 lines
948 B
Plaintext
50 lines
948 B
Plaintext
NAME
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head - create a list of specified size from the head of a list
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SYNOPSIS
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head(x, y)
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TYPES
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x list
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y int
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return list
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DESCRIPTION
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If 0 <= y <= size(x), head(x,y) returns a list of size y whose
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elements in succession have values x[[0]]. x[[1]], ..., x[[y - 1]].
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If y > size(x), head(x,y) is a copy of x.
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If -size(x) < y < 0, head(x,y) returns a list of size (size(x) + y)
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whose elements in succession have values x[[0]]. x[[1]], ...,
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i.e. a copy of x from which the last -y members have been deleted.
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If y <= -size(x), head(x,y) returns a list with no members.
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For any integer y, x == join(head(x,y), tail(x,-y)).
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EXAMPLE
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> A = list(2, 3, 5, 7, 11)
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> head(A, 2)
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list (2 members, 2 nonzero):
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[[0]] = 2
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[[1]] = 3
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> head(A, -2)
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list (3 members, 3 nonzero):
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[[0]] = 2
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[[1]] = 3
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[[2]] = 5
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LIMITS
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none
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LIBRARY
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none
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SEE ALSO
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tail, segment
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