I have a .dat file that shows results of a lab experiment at different conditions (you can find the dataset here). The data file is inhomogeneous, meaning that the number of rows and columns differ from one place to another, just as follows:
The dataset has also Table 2, Table 3, .. , Table 7.
So, what i need to do is to split this dataset into multiple files according to each table of records, i have tried the following code:
import pandas as pd
import os
f = open('BCZT015Fe_21-120.dat', 'r')
databaseRaw = f.read()
database = databaseRaw.split('Table ')
f.close()
for i in range(0, len(database) - 1) :
database[i] = 'Table '+''.join(database[i])
for i in range(0, len(database)) :
f = open("output" + str(i) + "" + ".csv" ,"w")
f.writelines(database[i])
f.close()
os.remove("output0.csv")
os.remove("output1.csv")
os.remove("output2.csv")
My idea here is trying to save the data in a list, and iterate over the whole database and whenever the word "table" is detected, I just split the data before and after. The problem with this approach is that the resulting files have the data stored into just one column (which is understandable since i am saving the dataset in just one list), so, how can i split such a dataset into multiple files and keep the data from the original file as it is in the separated files?
Hope someone could help me out with this problem, and Thank you in advance!
I need to process data measured every 20 seconds during the whole 2018 year, the raw file has following structure:
date time a lot of trash
in several rows
amount of samples trash again
data
date time a lot of trash
etc.
I want to make one pandas dataframe of it or at least one dataframe per every block (its size is coded as amount of samples) of data saving the time of measurement.
How can I ignore all other data trash? I know that it is written periodically (period = amount of samples), but:
- I don't know how many strings are in file
- I don't want to use explicit method file.getline() in cycle, because it would work just endlessly (especially in python) and I have no enough computing power to use it
Is there any method to skip rows periodically in pandas or another lib? Or how else can I resolve it?
There is an example of my data:
https://drive.google.com/file/d/1OefLwpTaytL7L3WFqtnxg0mDXAljc56p/view?usp=sharing
I want to get dataframe similar to datatable on the pic + additional column with date-time without technical rows
Use itertools.islice, where N below means read every N lines
from itertools import islice
N = 3
sep = ','
with open(file_path, 'r') as f:
lines_gen = islice(f, None, None, N)
df = pd.DataFrame([x.strip().split(sep) for x in lines_gen])
I repeated your data three times. It sounds like you need every 4th row (not starting at 0) because that is where your data lies. In the documentation for skipsrows it says.
If callable, the callable function will be evaluated against the row indices, returning True if the row should be skipped and False otherwise. An example of a valid callable argument would be lambda x: x in [0, 2].
So what if we pass a not in to the lambda function? that is what I am doing below.
I am creating a list of the values i want to keep. and passing the not in to the skiprows argument. In English, skip all the rows that are not every 4th line.
import pandas as pd
# creating a list of all the 4th row indexes. If you need more than 1 million, just up the range number
list_of_rows_to_keep = list(range(0,1000000))[3::4]
# passing this list to the lambda function using not in.
df = pd.read_csv(r'PATH_To_CSV.csv', skiprows=lambda x: x not in list_of_rows_to_keep)
df.head()
#output
0 data
1 data
2 data
Just count how many lines are in file and put the list of them (may it calls useless_rows) which are supposed to be skiped in pandas.read_csv(..., skiprows=useless_rows).
My problem was a chip rows counting.
There are few ways to do it:
On Linux command "wc -l" (here is an instruction how to put it into your code: Running "wc -l <filename>" within Python Code)
Generators. I have a key in my relevant rows: it is in last column. Not really informative, but rescue for me. So I can count string with it, appears it's abour 500000 lines and it took 0.00011 to count
with open(filename) as f:
for row in f:
if '2147483647' in row:
continue
yield row
I want to create a matrix from CSV file.
Here's what I've tried:
df = pd.read_csv('csv-path', usecols=[0,1], names=['A', 'B'])
pd.pivot_table(df,columns='A', values='B')
output : [9197337 rows x 2 columns].
I want to take fewer rows like I want to make a matrix of first 100 entries or 1000. How can I do that?
Since the csv module only deals in complete files, it would be easiest to extract the lines of interest before you use it. You could do this before running your program with the Unix head utility. Here's one way that should work in Python:
with open("csv-path") as inf, open("mod_csv_path", "w") as outf:
for i in range(1000):
outf.write(inf.readline())
Obviously you'd then read "mod_csv_path" rather than "csv-path' as the input file.
Pandas seems to be the right approach ? Can you provide a sample of your CSV file.
Also, with pandas, you can limit the size of your dataframe:
limited_df = df.head(num_elements)
I have a large text file, separated by semi-column. I am trying to retrieve the values of a column (e.g. the second column) and work on it iteratively using numpy. An example of data contained in a text file is given below:
10862;2;1;1;0;0;0;3571;0;
10868;2;1;1;1;0;0;3571;0;
10875;2;1;1;1;0;0;3571;0;
10883;2;1;1;1;0;0;3571;0;
...
11565;2;1;1;1;0;0;3571;0;
11572;2;1;1;1;0;0;3571;0;
11579;2;1;1;1;0;0;3571;0;
11598;2;1;1;1;0;0;3571;0;
11606;2;1;1;
Please note that the last line may not contain the same number of values as the previous ones.
I am trying to use pandas.read_csv to read this large file by chunks. For the purpose of the example, let's assume that the chunk size is 40.
I have tried so far 2 different approaches:
1)
Set nrows, and iteratively increase the skiprows so as to read the entire file by chunk.
nrows_set = 40
n_it = 0
while(1):
df = pd.read_csv(filename, nrows=nrows_set , sep=';',skiprows = n_it * nrows_set)
vect2 = df[1] # trying to access the values of the second column -- works
n_it = n_it+1
Issue when accessing the end of the file: Pandas generates an error when ones tries to read a number of rows bigger than the number of rows contained in the file.
For example, if the file contains 20 lines, and nrows is set as 40, the file cannot be read. My first approach hence generated a bug when I was trying to read the last 40 lines of my file, when less than 40 lines were remaining.
I do not know how to check for the end of file before trying to read from the file - and I do not want to load the entire file to obtain the total rows number since the file is large. Hence, I tried a second approach.
2)
Set chunksize. This works well, however I have an issue when I then try to acess the data in chunk:
reader = pd.read_csv(filename, chunksize=40, sep=';')
for chunk in reader :
print(chunk) # displays data -- the data looks correct
chunk[1] # trying to access the values of the second column -- generates an error
What is the data type of chunk, and how can I convert it so as this operation works?
Alternatively, how can I retrieve the number of lines contained in a file without loading the entire file in memory (solution 1))?
Thank you for your help!
Gaelle
chunk is a data frame.
so you can access it using indexers (accesors) like .ix / .loc / .iloc / .at / etc.:
chunk.ix[:, 'col_name']
chunk.iloc[:, 1] # second column
I'm having trouble with processing some csv data files for a project. Someone suggested using python/csv reader to help break down the files, which I've had some success with, but not in a way I can use.
This code is a little different from what I was trying before. I am essentially attempting to create an array. In the raw data format, the first 7 rows contain no data, and then each column contains 50 experiments, each with 4000 rows, for 200000 some rows total. What I want to do is take each column, and make it an individual csv file, with each experiment in its own column. So it would be an array of 50 columns and 4000 rows for each data type. The code here does break down the correct values, I think the logic is okay, but it is breaking down the opposite of how I want it. I want the separators without quotes (the commas and spaces) and I want the element values in quotes. Right now it is doing just the opposite for both, element values with no quotes, and the separators in quotes. I've spent several hours trying to figure out how to do this to no avail,
import csv
ifile = open('00_follow_maverick.csv')
epistemicfile = open('00_follower_maverick_EP.csv', 'w')
reader = csv.reader(ifile)
colnum = 0
rownum = 0
y = 0
z = 8
for column in reader:
rownum = 4000 * y + z
for element in column:
writer = csv.writer(epistemicfile)
if y <= 50:
y = y + 1
writer.writerow([element])
writer.writerow(',')
rownum = x * y + z
if y > 50:
y = 0
z = z + 1
writer.writerow(' ')
rownum = x * y + z
if z >= 4008:
break
What is going on: I am taking each row in the raw data file in iterations of 4000, so that I can separate them with commas for the 50 experiments. When y, the experiment indicator here, reaches 50, it resets back to experiment 0, and adds 1 to z, which tells it which row to look at, by the formula of 4000 * y + z. When it completes the rows for all 50 experiments, it is finished. The problem here is that I don't know how to get python to write the actual values in quotes, and my separators outside of quotes.
Any help will be most appreciated. Apologies if this seems a stupid question, I have no programming experience, this is my first attempt ever. Thank you.
Sorry, I'll try to make this more clear. The original csv file has several columns, each of which are different sets of data.
A miniature example of the raw file looks like:
column1 column2 column3
exp1data1time1 exp1data2time1 exp1data3time1
exp1data1time2 exp1data2time2 exp1data3time2
exp2data1time1 exp2data2time1 exp2data3time1
exp2data1time2 exp2data2time2 exp2data3time2
exp3data1time1 exp3data2time1 exp3data3time1
exp3data1time2 exp3data2time2 exp3data3time2
So, the actual version has 4000 rows instead of 2 for each new experiment. There are 40 columns in the actual version, but basically, the data type in the raw file matches the column number. I want to separate each data type or column into an individual csv file.
This would look like:
csv file1
exp1data1time1 exp2data1time1 exp3data1time1
exp1data1time2 exp2data1time2 exp3data1time2
csv file2
exp1data2time1 exp2data2time1 exp3data2time1
exp1data2time2 exp2data2time2 exp3data2time2
csv file3
exp1data3time1 exp2data3time1 exp3data3time1
exp1data3time2 exp2data3time2 exp3data3time2
So, I'd move the raw data in the file to a new column, and each data type to its own file. Right now I'm only going to do one file, until I can move the separate experiments to separate columns in the new file. So, in the code, the above would make the 4000 into 2. I hope this makes more sense, but if not, I will try again.
If I had a cat for each time I saw a bio or psych or chem database in this state:
"each column contains 50 experiments,
each with 4000 rows, for 200000 some
rows total. What I want to do is take
each column, and make it an individual
csv file, with each experiment in its
own column. So it would be an array of
50 columns and 4000 rows for each data
type"
I'd have way too farking many cats.
I didn't even look at your code because the re-mangling you are proposing is just another problem that will have to be solved. I don't fault you, you claim to be a novice and all your peers make the same sort of error. Beginning programmers who have yet to understand how to use arrays often wind up with variable declarations like:
integer response01, response02, response03, response04, ...
and then very, very redundant code when they try to see if every response is - say - 1. I think this is such a seductive error in bio-informatics because it actually models the paper notations they come from rather well. Unfortunately, the sheet-of-paper model isn't the best way to model data.
You should read and understand why database normalization was developed, codified and has come to dominate how people think about structured data. One Wikipedia article may not be sufficient. Using the example I excerpted let me try to explain how I think of it. Your data consists of observations; put the other way the primary datum is a singular observation. That observation has a context though: it is one of a set of 4000 observations, where each set belongs to one of 50 experiments. If you had to attach a context to each observation you'd wind up with an addressing scheme that looks like:
<experiment_number, observation_number, value>
In database jargon, that's a tuple, and it is capable of representing, with no ambiguity and perfect symmetry the entirety of your data. I'm not certain that I've understood the exact structure of your data, so perhaps it is something more like:
<experiment_number, protocol_number, observation_number, value>
where the protocol may be some form of variable treatment type - let's say pH. But note that I didn't call the protocol a pH and I don't record it as such in the database. What I would then need is an ancillary table showing the relevant parameters of the protocol, e.g.:
<protocol_number, acidity, temperature, pressure>
Now we've just built a "relation" that those database people like to talk about; we've also begun normalizing the data. If you need to know the pH for a given protocol, there is one and only one place to find it, in the proper row of the protocol table. Note that I've divorced the data that fit so nicely together on a data-sheet and from the observation table I can't see the pH for a particular dataum. But that's okay, because I can just look it up in my protocol table if needed. This is a "relational join" and if I needed to, I could coalesce all the various parameters from all the various tables and reconstitute the original datasheet in its original, unstructured glory.
I hope this answer is of some use to you. I'm certain that I don't even know what field of study your data is from, but these principles apply across domains from drug trials to purchase requisition processing. Please understand that I'm trying to inform, per your request, and there is zero condescension intended. I welcome further questions on the matter.
Normalization of the dataset
Thanks for giving the example. You have the context I described already, perhaps I can make it more clear.
column1 column2 column3
exp1data1time1 exp1data2time1 exp1data3time1
exp1data1time2 exp1data2time2 exp1data3time2
The columns are an artifice made by the last guy; that is, they carry no relevant information. When parsed into a normal form, your data looks just like my first proposed tuple:
<experiment_number, time, response_number, response>
where I suspect time may actually mean "subject_id" or "trial_number". It may very well look incongruous to you to conjoin all the different response values into the same dataset; indeed based on your desired output, I suspect that it does. At first blush, the objection "but the subject's response to a question about epistemic properties of chairs has no connection to their meta-epistemic beliefs regarding color", but this would be mistaken. The data are related because they have a common experimental subject, and self-correlation is an important concept in sociological analytics.
For example, you may find that respondent A gives the same responses as respondent B, except all of A's responses are biased one higher because of how the subject understood the criteria. This would make a very real difference in the absolute values of the data, but I hope you can see that the question "do A and B actually have different epistemic models?" is salient and valid. One method of data modeling allows this question to be answered easily, your desired method does not.
Working parsing code to follow shortly.
The normalizing code
#!/usr/bin/python
"""parses a csv file containing a particular data layout and normalizes
The raw data set is a csv file of the form::
column1 column2 column3
exp01data01time01 exp01data02time01 exp01data03time01
exp01data01time02 exp01data02time02 exp01data03time02
where there are 40 such columns and the literal column title
is added as context to the output row
it is assumed that the columns are comma separated but
the lexical form of the subcolumns is unspecified.
Output will consist of a single CSV output stream
on stdout of the form::
exp01, time01, data01, column1
for varying actual values of each field.
"""
import csv
import sys
def split_subfields(s):
"""returns a list of subfields of s
this function is expected to be re-written to match the actual,
unspecified lexical structure of s."""
return [s[0:5], s[5:11], s[11:17]]
def normalise_data(reader, writer):
"""returns a list of the column headings from the reader"""
# obtain the headings for use in normalization
names = reader.next()
# get the data rows, split them out by column, add the column name
for row in reader:
for column, datum in enumerate(row):
fields = split_subfields(datum)
fields.append(names[column])
writer.writerow(fields)
def main():
if len(sys.argv) != 2:
print >> sys.stderr, ('usage: %s input.csv' % sys.argv[0])
sys.exit(1)
in_file = sys.argv[1]
reader = csv.reader(open(in_file))
writer = csv.writer(sys.stdout)
normalise_data(reader, writer)
if __name__ == '__main__': main()
Such that the command python epistem.py raw_data.csv > cooked_data.csv yields excerpted output looking like:
exp01,data01,time01,column1
...
exp01,data40,time01,column40
exp01,data01,time02,column1
exp01,data01,time03,column1
...
exp02,data40,time15,column40