How to extract the following data from the file?

Question

Consider the following file. It has the form

HepMC::Version 2.06.09
HepMC::IO_GenEvent-START_EVENT_LISTING
E ...
N ...
U ...
C ...
V ...
P ... YY 0 0 XX 0
V ...
P ... 2 0 0 0 0
P ... 2 0 0 0 0
P ... 1 0 0 0 0
P ... 1 0 0 0 0
E ...
...

Could you please tell me how to extract only the rows

E ...

and those starting from P with

P ... 1 0 0 0 0

This is how I tried to do it:

file = Import["tag_1_pythia8_events.hepmc", "Table"];
Cases[file, {"E", __} || {__, 1, 0, 0, 0, 0}]

But I do not know the syntax well: the "||" construction does not work.

Answer 1

In a method very similar to what I did here, I split the data by newlines, and find all line numbers that either start with "E" or "P ... 1 0 0 0 0"

splitData = StringSplit[data, "\n"];
pTest = "P ... 1 0 0 0 0";
l = pTest // StringLength;
firstLetters = StringTake[splitData, 1];
moreLetters = StringTake[splitData, {1, l}];

ePos = Flatten[Position[firstLetters, "E"]];
pPos = Flatten[Position[moreLetters, pTest]];
allPos = Join[ePos, pPos] // Sort
(*{3, 12, 13, 14}*)

and then just grab each of those lines from splitData:

splitData[[allPos]]
(*{"E ...", "P ... 1 0 0 0 0", "P ... 1 0 0 0 0", "E ..."}*)

Answer 2

Building up on the comment from @LouisB:

file = Import["C:/tag_1_pythia8_events.hepmc", "Table"];
SequenceCases[file, {{"E", ___}} | {{"P", ___, 1, 0 ..}}]