Question

36) 'readings.txt' is a file that contains 10,000 integer readings from a radiation counter. The lowest reading should be 0. The radiation counter occasionally malfunctions and records a negative number Describe how you would write a segment of code that will determine how many times the radiation counter malfunctioned when making those 10,000 readings. How would you do it if you used a dictionary? How would you do it if you did not use a dictionary?

Answer 1

SOLUTION

Before I start I have assumed a few things that aren't mentioned in the problem which I'm specifying in the beginning. Since how the numbers are stored in the file i.e. the delimiter is not specified , I'm assuming that it's being separated by a ',' . Hence making readings.txt looks like : 1,2,3,4,... Therefore we will read the file using the open and split function :

f.read() reads the file content and store it in as a string while the split method splits the strings by using a delimiter, which is ',' in this case . So if the contents of file are 1,2,3,4,5 ,

f.read() will read it all as a single string as '1,2,3,4,5' and split() function will split this string by ',' and convert it to a list as ['1','2','3','4','5'] so its also important to convert all the numbers to int before performing any actions on them.

Code snippet for reading file

f=open("readings.txt","r")

for i in f.read().split(","):     

         #Do something

LOGIC

The questions asks us to count the number of negatives in the file , which is the number of malfunctions by the radiator.

1) USING DICTIONARY

my_dict={'negative':0}
for i in f.read().split(","):
    if int(i)<0:
        my_dict['negative']+=1
print(my_dict['negative'])

Dictionary in python consists of Key and Value(s). We are required to keep a count of negatives in our dictionary therefore I initialized a dictionary called 'my_dict' with a key value pair as 'negative' and 0. Negative is the key to the number of negatives in the text file and we will increase the number as soon we find more negatives in the file. For each element we type case it to int whose reason I've provided above and check if it's lesser than 0. If the number is less than 0 we perform an increment to the 'Negative' value of dictionary by 1 and check the other element. In the end the value for the key 'negative' will be the count of malfunctions happened by the radiator.

2) WITHOUT USING DICTIONARY

r=[int(i) for i in (f.read()).split(",")]
negative=len([i for i in r if i<0])
print(negative)

I've used list comprehension in this part a lot. As we know that the read() function read the contents of a file as a single string and then the split function splits the string by ',' and we get a list of elements which are numbers but are as strings i.e. ['1','2','3','4',....] .

Therefore to change them to integer I did that using list comprehension using:

r=[int(i) for i in (f.read()).split(",")]

It says that for i in the list ['1','2','3','4','5',....] , which is being processed by read() and split() function convert it to int(i) and put all of it in a list. The result are always written in the beginning that is int(i) in this case , then the loop and the conditions which is not present in this case. Therefore this statement will give us :

[1,2,3,4,5....]

Since now we have a list of integers we need to keep only those which are negatives and count them therefore again using list comprehension:

negative=len([i for i in r if i<0])

The statements says that we want the length of the list .The list is i for i in the list r and if the element i is less than 0 then keep it. The output we want is the element i and the loop is in the elements for r and condition is if i<0. It simply says make a list of those elements in r which are less than 0 and tell me the length / count of that list.

Complete Code for the problem

f=open("readings.txt","r")
#using dictionary
d={'negative':0}
for i in f.read().split(","):
    if int(i)<0:
        d['negative']+=1
print(d['negative'])
f=open("readings.txt","r")
#without using dictionary
r=[int(i) for i in (f.read()).split(",")]
negative=len([i for i in r if i<0])
print(negative)

Hope this helps!