How to get particular values

Hi, I have a data set like this

    x1    y1   y2    y3    y4    y5  ................
    x2    z1   z2    z3    z4    z5  ''''''''''''''''
    x3    like this it continues
    x4
    .

    x1
    x2
    x3
    x4
    .

I need to pick up all z values for x4, y3, how to start wuth thanks in advance.

[Geoff Hayes]

Mohana - I think you need to provide more details on the pattern. Why do the y's follow x1, but the z's follow x2? What follows x3?

[Guillaume]

Assuming you've read your text file. How have you stored the data?

In three matrices, one 1*m for x, one n*1 for y and one m*n for z? or something else?