GAP (Utils) - Chapter 2: Printing Lists and Iterators

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2 Printing Lists and Iterators
2.1 Printing selected items
2.1-1 PrintSelection

### 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 PrintSelection

`‣ PrintSelection`( obj, list ) | ( function )

`‣ PrintSelection`( obj, first, step[, last] ) | ( 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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