Re: newbie list question

*To*: mathgroup at smc.vnet.net*Subject*: [mg115003] Re: newbie list question*From*: Peter Pein <petsie at dordos.net>*Date*: Tue, 28 Dec 2010 06:49:05 -0500 (EST)*References*: <if70bt$330$1@smc.vnet.net>

On 26.12.2010 10:02, Gareth Edwards wrote: > Hi, > > Liking Mathematica a lot, but struggling with the early part of the learning curve, i.e. don't know what I don't know... > > What would be the neatest syntax for finding the first location of elements from one list in another? For example: > > listA = { 4,5,8,2,6,4 } > listB = { 8,4,2 } > > > I would like a function to return {3,1,4} in this case (the first location in A of each element in B) > > Many thanks! > Hi Gareth, Use Position to get the first location of a number in level 1 of listA Position[listA,number,1,1] this will give {{pos. of nr.}}. Now build an anonymous function and map that on listB. Flatten the result to get rid of unnecessary nested lists: Position[listA, #1, 1, 1] & /@ listB // Flatten wil give {3,1,4} as result. Regards, Peter