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    <p>This method traverses the list at most twice:</p> <pre><code>(define (swap-index index1 index2 lst) ;; FIND-ELEMENTS -- ;; INPUT: count, an integer; lst, a list ;; OUTPUT: a pair of the form '(a . b) (define (find-elements count lst) (cond ((null? lst) '()) ; really, we should never reach this if indices are valid ((= count index1) ; found the first element, so hold on to it while we look for the next one (cons (car lst) (find-elements (+ 1 count) (cdr lst)))) ((= count index2) (car lst)) ; found the second element, return part 2 of the pair (else ; since we only care about 2 elements we can just skip everything else (find-elements (+ 1 count) (cdr lst))))) ;; BUILD-LIST -- ;; INPUT: count, an integer; elements, a pair; lst, a list ;; OUTPUT: a new list (define (build-list count elements lst) (cond ((null? lst) '()) ; again, we shouldn't get here if indices are valid ((= count index1) ; reached first index, substitute 2nd element and keep going (cons (cdr elements) (build-list (+ 1 count) elements (cdr lst)))) ((= count index2) ; reached second index, substitute 1st element and stop (cons (car elements) (cdr lst))) (else ; everything else just gets added to the list per usual (cons (car lst) (build-list (+ 1 count) elements (cdr lst)))))) (build-list 0 (find-elements 0 lst) lst)) ; call build-list using a call to find-elements as a parameter </code></pre> <p>First, <code>find-elements</code> looks through the list and returns a <code>cons</code>'d pair of the elements that we want to swap. <strong>Note:</strong> this code depends on the assumption that the indices are given in order so that the smallest is first.</p> <p>Next, <code>build-list</code> takes the output from <code>find-elements</code> so that during our next traversal we can substitute the appropriate element.</p>
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    1. POSwap two elements in list in Scheme
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Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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