Second level depth pure function?

Question

I have the following working construction:

Select[ln125, # == Nearest[ln125, 551.748][[1]] &]

Here, ln125 is a one dimensional list.

What I want further is to apply this construction not only to ln125, for example, but for a list of {ln125,ln126,ln127}.

Let's say,

f[list_]:=Select[list, # == Nearest[list, 551.748][[1]] &]

I want to do this:

f /@ {ln125,ln126,ln127}.

The question is: is it possible to acheive my goal only using pure functions? That is, without defining dummy function (f in my case)? The problem is that definition of f already has pure function (as a criteria for Select) and, thus, there should be two pure function of different depths (don't know how to name it correctly) at once. In other words, I want to turn the list variable into # but in a way that Mathematica can distinguish which # goes with each different pure function.

Answer 1

In can be done in a terse way with nested pure functions:

lists = RandomReal[{0, 10}, {3, 10}]

{{3.35338, 2.82572, 0.152277, 1.19036, 9.88211, 6.55398, 8.11855, 0.793288, 9.04547, 6.42518}, {4.95417, 7.73982, 5.58323, 3.09912, 5.44546, 8.88474, 2.67437, 8.20605, 4.55918, 1.95303}, {2.53793, 6.67839, 8.71033, 8.4877, 0.634367, 7.99796, 4.74131, 0.679337, 8.29468, 9.91209}}

Select[#, With[{aList = #}, # == Nearest[aList, 5.][[1]] &]] & /@ lists

{{6.42518}, {4.95417}, {4.74131}

Using With to insert expressions into Function, which has the HoldAll attribute, is trick that is useful to keep in mind.

Answer 2

You can use the form Function[{x,y,z}, body] to define a pure function with formal parameters x,y,z ( see Documentation >> Function)

Let

 lists = {ln125, ln126, ln127} = RandomReal[{0, 10}, {3, 10}]
 (* {{1.72286, 5.24912, 8.87257, 5.77593, 6.31276, 1.77914, 2.06393,
      0.328725, 9.46436, 4.96257}, 
     {1.71171, 2.54337, 5.93807, 9.46774,  6.99601, 2.76927, 7.58995,
      1.25785, 2.09789, 9.32326}, 
     {6.9821, 8.62002, 2.0763, 8.9402, 4.36728, 3.8571, 4.4175,
      7.15698, 7.64633, 5.23772}} *)

Define, (with 4. playing the role of 551.748 in your example):

 f2 = Function[{x}, Select[x, # == Nearest[x, 4.][[1]] &]]
 f2 /@ lists
 (* {{4.96257}, {2.76927}, {3.8571}} *)   

or

  f3 = With[{temp = Nearest[#1, 4.`][[1]]}, Select[#1, # == temp &]] &
  f3 /@ lists
  (* {{4.96257}, {2.76927}, {3.8571}} *)