Using np.loadtxt between two specific lines (Python 2.7)

Question

I know that np.loadtxt allows you to quickly extract data from columns in a text file, and I know that you can use skiprows to skip the first N number of rows. Can you specify an end line number, such that np.loadtxt only extracts text between two known line numbers in a text file?

In the following example, you can specify:

(dat1,dat2) = np.loadtxt(file, skiprows = 1, usecols = (0,1), unpack=True)

but I get an error saying that "ValueError: could not convert string to float: Data1"

Example: 1 Data1 Data2 Data3 2 1 3 5 3 7 1 6 [...] 48 8 9 2 49 2 7 6 50 Data1 Data2 Data3 51 5 6 1 52 9 12 3 53 1 0 2

Answer 1

np.genfromtxt with

skip_header : int, optional
    The number of lines to skip at the beginning of the file.
skip_footer : int, optional
    The number of lines to skip at the end of the file.
max_rows : int,  optional
    The maximum number of rows to read. Must not be used with skip_footer
    at the same time.  If given, the value must be at least 1. Default is
    to read the entire file.

gives a lot of control over which lines are read.

Another option is to open the file yourself, eg

with open('myfile', 'rb') as f:
     <skip>
     np.genfromtxt(f, ...)
     etc

and pass it to genfromtxt . You can even feed it line by line. genfromtxt (and loadtxt ) is happy with anything that feeds it lines - a file, a list of lines, a generator of lines, etc.