Shell Programming and Scripting

This is a filter, so it processes one line at a time. Let's take the first line of input:

Code:

Abc-01    pc1    -0.69

We make an assignment

Code:

a[$1]=$3; e.i. a["Abc-01"]=-0.69

Next line of input:

Code:

Abc-01    E2cR    0.459666666666667

Is $1 in array a? Yes, we do have a["Abc-01"] defined. Append 3rd column. Now we have

Code:

a["Abc-01"]=-0.69       0.459666666666667

Next line of input is gonna make a["Abc-01"] grow into '-0.69\t0.459666666666667\t1.2265625', which is the desired output.
Next line will set array element a["Xyz-01"], etc.
You are constructing array 'a' so that the elements of it are your desired output; each array element has one line of output stored.
After you have all lines processed, you have your array 'a' populated, and you are ready to print it; easy loop (although in random order!) will print what's stored in 'a'.