Joining lines, modulo the number of records - bash

Question

Say my stream is x*N lines long, where x is the number of records and N is the number of columns per record, and is output column-wise. For example, x=2, N=3:
1
2
Alice
Bob
London
New York
How can I join every line, modulo the number of records, back into columns:
1 Alice London
2 Bob New York
If I use paste, with N -s, I get the transposed output. I could use split, with the -l option equal to N, then recombine the pieces afterwards with paste, but I'd like to do it within the stream without spitting out temporary files all over the place.
Is there an "easy" solution (i.e., rather than invoking something like awk)? I'm thinking there may be some magic join solution, but I can't see it...
EDIT Another example, when x=5 and N=3:
1
2
3
4
5
a
b
c
d
e
alpha
beta
gamma
delta
epsilon
Expected output:
1 a alpha
2 b beta
3 c gamma
4 d delta
5 e epsilon

Answer 1

You are looking for pr to "columnate" the stream:
pr -T -s$'\t' -3 <<'END_STREAM'
1
2
Alice
Bob
London
New York
END_STREAM
1 Alice London
2 Bob New York
pr is in coreutils.

Answer 2

Most systems should include a tool called pr, intended to print files. It's part of POSIX.1 so it's almost certainly on any system you'll use.
$ pr -3 -t < inp1
1 a alpha
2 b beta
3 c gamma
4 d delta
5 e epsilon
Or if you prefer,
$ pr -3 -t -s, < inp1
1,a,alpha
2,b,beta
3,c,gamma
4,d,delta
5,e,epsilon
or
$ pr -3 -t -w 20 < inp1
1 a alpha
2 b beta
3 c gamma
4 d delta
5 e epsilo
Check the link above for standard usage information, or man pr for specific options in your operating system.

Answer 3

In order to reliably process the input you need to either know the number of columns in the output file or the number of lines in the output file. If you just know the number of columns, you'd need to read the input file twice.
Hackish coreutils solution
# If you don't know the number of output lines but the
# number of output columns in advance you can calculate it
# using wc -l
# Split the file by the number of output lines
split -l"${olines}" file FOO # FOO is a prefix. Choose a better one
paste FOO*
AWK solutions
If you know the number of output columns in advance you can use this awk script:
convert.awk:
BEGIN {
# Split the file into one big record where fields are separated
# by newlines
RS=''
FS='\n'
}
FNR==NR {
# We are reading the file twice (see invocation below)
# When reading it the first time we store the number
# of fields (lines) in the variable n because we need it
# when processing the file.
n=NF
}
{
# n / c is the number of output lines
# For every output line ...
for(i=0;i<n/c;i++) {
# ... print the columns belonging to it
for(ii=1+i;ii<=NF;ii+=n/c) {
printf "%s ", $ii
}
print "" # Adds a newline
}
}
and call it like this:
awk -vc=3 -f convert.awk file file # Twice the same file
If you know the number of ouput lines in advance you can use the following awk script:
convert.awk:
BEGIN {
# Split the file into one big record where fields are separated
# by newlines
RS=''
FS='\n'
}
{
# x is the number of output lines and has been passed to the
# script. For each line in output
for(i=0;i<x;i++){
# ... print the columns belonging to it
for(ii=i+1;ii<=NF;ii+=x){
printf "%s ",$ii
}
print "" # Adds a newline
}
}
And call it like this:
awk -vx=2 -f convert.awk file