Import data from first/last 100 rows of a file

Question

If one wants import data from the first three rows of a file "myfile.data", one can use the command

Import["myfile.data",{"Data",{1,2,3},All}];

However, if I want import the first 100 rows of the file, is there a quick way besides

Import["myfile.data",{"Data",{1,2,3,4,5,....},All}];

And what about the case I need import the last 100 rows of the file?

Answer 1

To import the first 100 rows of the file you can use

Import["myfile.data", {"Data", Range[100]}]

and to import the last 100 rows

Import["myfile.data", {"Data", -Range[100]}]

or

Import["myfile.data", {"Data", Range[-100,-1]}]

Answer 2

I encourage you to use the following command:

Import["file_name.txt", "Table"][[All, ;;100]]

It works by default with any structured data, while "Data" doesn't. And what's more important - surprisingly it works much faster than importing separated rows or columns - time difference could be the 10-100 times for huge files.

And eventually it's much easier to point what you really want to import with this usual mathematica notation, e.g. take first 5 cols and 100 last rows:

Import["file_name.txt", "Table"][[;;5, -100;;]]

Answer 3

Use the function 'take'

for example

list = Import["myfile.data",{"Data",{1,2,3},All}];

Take[list1, 100]

you will get the first hundred values

Take[list1, {100,200)]

you wil gett the values hundred until twohundred