too many values to unpack in genfromtxt

Question

I have a tsv file containing vibration data (with commas in place of dots for some silly reason, hence the converter). I'd like to generate numpy arrays from two of these channels, but get a "ValueError: too many values to unpack (expected 2)" that I can't figure out.

in ipython (with pylab option):

In [171] import re

In [172]: def qdsub(s):
   .....:     return re.sub('\,', '.', str(s)[2:-1])
   .....:

In [173]: x, y = genfromtxt('QD1_short.tsv', delimiter='\t', usecols=(0, 1), 
   .....: unpack=True, skip_header=13, converters={0:qdsub, 1:qdsub}, 
   .....: skip_footer=2, dtype=float)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-177-e17389233ac3> in <module>()
        1 x, y = genfromtxt('QD1_short.tsv', delimiter='\t', usecols=(0, 1), 
        2 unpack=True, skip_header=13, converters={0:qdsub, 1:qdsub},
  ----> 3 skip_footer=2, dtype=float)

ValueError: too many values to unpack (expected 2)

Apparently I can't answer my own question yet, but the problem is solved, see comment on User's answer — sjp, Nov 20 '13 at 12:04

score 1 · Answer 1 · answered Nov 20 '13 at 11:24

1

Maybe this is the problem:

x, y = ge...

Try

v = ge...

Example:

>>> a, b = [1,2,3,4]

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    a, b = [1,2,3,4]
ValueError: too many values to unpack

answered Nov 20 '13 at 11:24

User

14,131
2
40
59

well, `v = genfromtxt(...` certainly returns something, without errors, problem is it's a seemingly useless `array([('', ''), ('', ''), ('', ''), ..., ` using only one column, I get a neat array of floats, and I want to get two of those. I've done it before with x, y = loadtxt(... but the footer of this tsv means I cannot go that route – sjp Nov 20 '13 at 11:48
Apparently, the problem was in the converter. Modified it to `return re.sub('\,', '.', str(s)[2:-1])` and now it all works stellar. Seems strange that it was ok on single columns before though. Oh well.. – sjp Nov 20 '13 at 12:02

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

The documentation of numpy.genfromtxt says:

unpack : bool, optional

If True, the returned array is transposed, so that arguments may be unpacked 
using x, y, z = loadtxt(...)

My best guess is that you should try to wrap the genfromtxt inside loadtxt:

from numpy import loadtxt, genfromtxt
(...)

x, y = loadtxt(genfromtxt('QD1_short.tsv', delimiter='\t', usecols=(0, 1), 
                          unpack=True, skip_header=13, converters={0:qdsub, 1:qdsub}, 
                          skip_footer=2, dtype=float))

score 0 · Accepted Answer · answered Nov 21 '13 at 07:35

0

The problem was in the converter, which apparently should return a float

def qdsub(s):
    return float(re.sub('\,', '.', str(s)[2:-1]))

answered Nov 21 '13 at 07:35

sjp

382
4
15

too many values to unpack in genfromtxt

3 Answers3