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### 2 Printing Lists and Iterators

#### 2.1 Printing selected items

The functions described here print lists or objects with an iterator with one item per line, either the whole list/iterator or certain subsets:

• by giving a list of positions of items to be printed, or

• by specifying a first item and then a regular step.

##### 2.1-1 PrintOneItemPerLine
 ‣ PrintOneItemPerLine( obj ) ( function )

This function prints lists, or objects which have an iterator, vertically, rather than horizontally, may be useful when the entries are lengthy. Since a very similar result may be achieved using the GAP library functions Perform and Display, this function should be considered obsolete and liable to removal in due course.


gap> s3 := SymmetricGroup( 3 );;
gap> L := KnownPropertiesOfObject( GeneratorsOfGroup( s3 ) );;
gap> Perform( L, Display );
IsFinite
IsSmallList
IsGeneratorsOfMagmaWithInverses
IsGeneratorsOfSemigroup
IsSubsetLocallyFiniteGroup
gap> Perform( s3, Display );
()
(2,3)
(1,3)
(1,3,2)
(1,2,3)
(1,2)



##### 2.1-2 PrintSelection
 ‣ PrintSelection( obj, first, step[, last] ) ( function )
 ‣ PrintSelection( obj, list ) ( function )

This function, given three (or four) parameters, calls operations PrintSelectionFromList or PrintSelectionFromIterator which prints the first item specified, and then the item at every step. The fourth parameter is essential when the object being printed is infinite.

Alternatively, given two parameters, with the second parameter a list L of positive integers, only the items at positions in L are printed.


gap> L := List( [1..20], n -> n^5 );;
gap> PrintSelection( L, [18..20] );
18 : 1889568
19 : 2476099
20 : 3200000
gap> PrintSelection( L, 2, 9 );
2 : 32
11 : 161051
20 : 3200000
gap> PrintSelection( L, 2, 3, 11 );
2 : 32
5 : 3125
8 : 32768
11 : 161051
gap> s5 := SymmetricGroup( 5 );;
gap> PrintSelection( s5, [30,31,100,101] );
30 : (1,5)(3,4)
31 : (1,5,2)
100 : (1,4,3)
101 : (1,4)(3,5)
gap> PrintSelection( s5, 1, 30 );
1 : ()
31 : (1,5,2)
61 : (1,2,3)
91 : (1,3,5,2,4)
gap> PrintSelection( s5, 9, 11, 43 );
9 : (2,5,3)
20 : (2,4)
31 : (1,5,2)
42 : (1,5,2,3,4)


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