Follow-up to "Plot, extract data to file"

Question

This is literally a follow-up to part of Mr.Wizard’s answer to: Plot, extract data to a file

Specifically in reference to

multidat = Cases[First @ gr, Line[data_] :> data, -4];

We could then export each part to a separate file like this:

Export["file" <> IntegerString[#2] <> ".txt", #, "Table"] & ~MapIndexed~ multidat

{"file1.txt", "file2.txt", "file3.txt"}

First, may I please get confirmation that I’m correctly reading the ~s in the middle line as the infix version of

MapIndexed[Export["file" <> IntegerString[#2] <> ".txt", #, "Table"]&, multidat]

?

Second, is there a simple way to export multidat into a single file with the lines as pairs of columns? I.e., suppose multidat is

{{{a1,a2},{b1,b2},{c1,c2}},
 {{p1,p2},{q1,q2},{r1,r2},{s1,s2}},
 {{x1,x2},{y1,y2},{z1,z2}}}

How would you turn that into

{{a1,a2,p1,p2,x1,x2},
 {b1,b2,q1,q2,y1,y2},
 {c1,c2,r1,r2,z1,z2}},
 {,,s1,s2,,}}

?

Admittedly, I’m not sure how Mma would handle that last row. The data I have in mind is destined for a spreadsheet-like presentation where cells can be empty. Thanks for your help!

export list manipulation plotting

Natas · Answer

Firstly, you are right about Infix as a very short experiment can verify. I will not comment on this further.
x ~ f ~ y === f[x, y]

Regarding the reshaping of your data, let me walk you through a possible solution.
l = {
  {{a1, a2}, {b1, b2}, {c1, c2}},
  {{p1, p2}, {q1, q2}, {r1, r2}, {s1, s2}},
  {{x1, x2}, {y1, y2}, {z1, z2}}
}

Firstly, you probably will want to pad the list, such that the array is rectangular. I suggest here the padding {"", ""}. However, other paddings might be more suitable for your problem.
lPadded = PadRight[#, Max[Length[#] & /@ l], {{"", ""}}] & /@ l;

Then you can use Flatten to transpose everything to the form you want.
lReshaped = Flatten[lPadded, {{2}, {1, 3}}];

Finally, you can export the resulting list.
Export["mydata.csv", lReshaped]

kglr · Answer

Join[##, 2] & @@ PadRight[multidat, Automatic, ""]

{{a1, a2, p1, p2, x1, x2}, {b1, b2, q1, q2, y1, y2}, {c1, c2, r1, r2, z1, z2}, 
 {"", "", s1, s2, "", ""}}

Alternatively,
MapAt[ArrayPad[#, 2, ""] &, Join[##, 2] & @@ multidat, {-1}]

{{a1, a2, p1, p2, x1, x2}, {b1, b2, q1, q2, y1, y2}, {c1, c2, r1, r2, z1, z2},
  {"", "", s1, s2, "", ""}}

Follow-up to "Plot, extract data to file"

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