I am trying to take input from sys.stdin. This is a map reducer program for hadoop. Input file is in txt form. Preview of the data set:
196 242 3 881250949
186 302 3 891717742
22 377 1 878887116
244 51 2 880606923
166 346 1 886397596
298 474 4 884182806
115 265 2 881171488
253 465 5 891628467
305 451 3 886324817
6 86 3 883603013
62 257 2 879372434
286 1014 5 879781125
200 222 5 876042340
210 40 3 891035994
224 29 3 888104457
303 785 3 879485318
122 387 5 879270459
194 274 2 879539794
291 1042 4 874834944
Code that I have been trying -
import sys
df = pd.read_csv(sys.stdin,error_bad_lines=False)
I have also tried with delimiter = \t, header=False,defining column name
Nothing seems to work, the error I am getting is this error:
[root@sandbox lab]# cat /root/lab/u.data | python /root/lab/mid-1-mapper.py |python /root/lab/mid-1-reducer.py
Traceback (most recent call last):
File "/root/lab/mid-1-reducer.py", line 8, in <module>
df = pd.read_csv(sys.stdin,delimiter='\t')
File "/opt/rh/python27/root/usr/lib64/python2.7/site-packages/pandas/io/parsers.py", line 645, in parser_f
return _read(filepath_or_buffer, kwds)
File "/opt/rh/python27/root/usr/lib64/python2.7/site-packages/pandas/io/parsers.py", line 388, in _read
parser = TextFileReader(filepath_or_buffer, **kwds)
File "/opt/rh/python27/root/usr/lib64/python2.7/site-packages/pandas/io/parsers.py", line 729, in __init__
self._make_engine(self.engine)
File "/opt/rh/python27/root/usr/lib64/python2.7/site-packages/pandas/io/parsers.py", line 922, in _make_engine
self._engine = CParserWrapper(self.f, **self.options)
File "/opt/rh/python27/root/usr/lib64/python2.7/site-packages/pandas/io/parsers.py", line 1389, in __init__
self._reader = _parser.TextReader(src, **kwds)
File "pandas/parser.pyx", line 538, in pandas.parser.TextReader.__cinit__ (pandas/parser.c:5896)
pandas.io.common.EmptyDataError: No columns to parse from file
However, if when I try this directly in python(not in hadoop), it works fine.
I have tried to looked into stackoverflow posts, one of the post suggested try and except. Applying that leaves me with a empty file. Can anybody help? Thanks
Using try and except just lets you continue in spite of errors and handle them. It won't magically fix your errors.
read_csv
expects csv
files, which your input is obviously not. A quick look into the documentation:
delim_whitespace : boolean, default False
Specifies whether or not whitespace (e.g. ' ' or ' ') will be used as the sep. Equivalent to setting sep='+s'. If this option is set to True, nothing should be passed in for the delimiter parameter.
This seems like the right argument. Use
pandas.read_csv(filepath_or_buffer, delim_whitespace=True).
Using delimiter='\t'
should also work, unless the tabs are expanded (replaced by spaces). As we can't really tell, delim_whitespace
seems to be the better option.
If this doesn't help, just print out your sys.stdin
to check if you properly pass the text.
Edit: I just saw that you use
cat /root/lab/u.data | python /root/lab/mid-1-mapper.py |python /root/lab/mid-1-reducer.py
Is this intended, this way mid-1-reducer.py
processes the output of mid-1-mapper.py
. If you want to process the content of the file u.data
consider reading the file and not sys.stdin
.