Python for Beginners

# Task 1

Read a space separated file using Python.

1 0.296275
2 0.290138
3 0.299182
4 0.286541
5 0.294814
6 0.287718
7 0.289807
8 0.279831
9 0.325793

#Code

>> f = open(‘test.txt’, ‘r’)
>>> for line in f:
…           line = line.strip()
…           columns = line.split()
…           time = columns[0]
…          dist = float(columns[1])
…          print(time, dist)

So if the file has a header

#Time distance
1 0.296275
2 0.290138
3 0.299182
4 0.286541
5 0.294814
6 0.287718
7 0.289807
8 0.279831
9 0.325793

Here is the code

>>>f = open('test.txt', 'r')
#Remove the header
>>> header1 = f.readline()
>>> for line in f:
...     line = line.strip()
...     columns = line.split()
...     time = columns[0]
...     dist = float(columns[1])
...     print(time, dist)

 

# If Column 2 > cutoff print out the corresponding Column 1

#Using Pandas
import pandas as pd
df = pd.read_csv('test.txt', sep=' ', header=None)
print (df[df[1]>0.29][0])

#Output

0 1
1 2
2 3
4 5
8 9

#Alternative

>>> f = open('test.txt', 'r')
>>> for line in f:
...     line = line.strip()
...     columns = line.split()
...     time = columns[0]
...     dist = float(columns[1])
...     if dist > 0.29:
...        print(time)

#Correlation coefficient between two columns

#Input (coor.txt)

2 3
3 6
4 9
5 12
6 15
7 21
8 24
9 27

# Command

import pandas as pd
df = pd.read_csv('coor.txt', sep=' ', header=None)
df[0].corr(df[1])

# Introduction to function

The following is our dataset named test.txt (this dataset has header)

#Time dist
1 0.296275
2 0.290138
3 0.299182
4 0.286541
5 0.294814
6 0.287718
7 0.289807
8 0.279831
9 0.325793

The aim is to write a function which will do the following:

If Column 2 > cutoff print out the corresponding Column 1 else print out the values of column 2

#Code

>>> f = open('test.txt', 'r')
>>> header1 = f.readline()
>>> for line in f:
...     line=line.strip()
...     columns=line.split()
...     time=columns[0]
...     dist=float(columns[1])
...     def is_cutoff(input_list):
...         if input_list > 0.29:
...            return time
...         else:
...            return dist
...      bhakat_data = is_cutoff(dist)
...      print(bhakat_data)

#Output

1
2
3
0.286541
5
0.287718
0.289807
0.279831
9

# Task: Reshape a list into a 2*3 column using pandas

#Code

a=[-0.26087587488489344,-0.5473357965371729,-0.27654025363442625,1.404881305053428,-0.018092484992362462,0.12383162178724855]
len(a)
s = pd.DataFrame(np.array(a).reshape(2,3), columns = list("abc"))
print (s)

# Outcome

          a         b         c
0 -0.260876 -0.547336 -0.276540
1  1.404881 -0.018092  0.123832

# List to column (with two decimal points in the output)

#Code

import pandas as pd
a=[-0.26087587488489344,-0.5473357965371729]
df = pd.Series(a)
df = df.round(2)

# Output

>>> df
0 -0.26
1 -0.55

# Task: Selecting multiple columns using pandas

The dataset looks like

0.000000 0.287274 0.281606
1.000000 0.296275 0.278471
2.000000 0.290138 0.265047
3.000000 0.299182 0.282561
4.000000 0.286541 0.285144

#Code

import pandas as pd
df = pd.read_csv('test_colvar.dat', sep=' ', header=None)
df1 = df.iloc[:,0:2] #this selects first and the second column
df1 = df.iloc[:,1:3] #this selects second and the third column

#Output
> df1
0 1
0 0.0 0.287274
1 1.0 0.296275
2 2.0 0.290138
3 3.0 0.299182
4 4.0 0.286541

# Task: Deleting specific column using pandas

Using the same dataset as the previous task.

# Code

import pandas as pd
df = pd.read_csv('test_colvar.dat', sep=' ', header=None)
df.drop(df.columns[[0, 1]], axis=1) # Removing the first and the second column

# Task: Convert a column to a space separated list

My dataset consists of a single column named tmp

893
896
899
902
905
908
911
914
917
920

We will use pandas to convert this column to space separated list

# Code

import pandas as pd
df = pd.read_csv('tmp', sep=' ', header=None)
list = df[0].tolist() #this converts it to a comma seperated list
" ".join([str(i) for i in list]) #this converts it to a space separated list

Output

'893 896 899 902 905 908 911 914 917 920'