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I have a list {a,b,c,d} and a second list where is how many times the elements of the first list repeat {1,4,2,6} (the order is according with the first list). Then I need to create a third list with this information: {a,b,b,b,b,c,c,d,d,d,d,d,d}. What can I do?

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marked as duplicate by Kuba list-manipulation Mar 22 '18 at 7:02

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Catenate @ MapThread[ConstantArray, {{a, b, c, d}, {1, 4, 2, 6}}]

{a, b, b, b, b, c, c, d, d, d, d, d, d}

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  • $\begingroup$ I'm leaving my answer but please vote for this instead (ht kglr). $\endgroup$ – Alan Mar 22 '18 at 2:29
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    $\begingroup$ Catenate not needed. Flatten@MapThread[ConstantArray, {{a, b, c, d}, {1, 4, 2, 6}}] works. Has advantage of working in older versions without Catenate. $\endgroup$ – m_goldberg Mar 22 '18 at 3:06

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