How to replace an element of an array in a specific way-CodePudding

I'm solving a problem with this concept: It is a classroom, and I have to replace an available seat with a name, but in a specific way: it is replaced in the last row, from right to left. If the classroom is full it will show a message that there are no places available.

I have no idea how to replace an available seat in the order that the problem says.

import numpy as np

classroom1 = np.array([["Martha", "Available"], 
                       ["Max", "Anahi"], 
                       ["Available", "Available"], 
                       ["Alexis", "Rigel"]])

So far I can replace a seat of my choice manually, but not in the way the problem states. for example:

classroom1[0,1] = "Alex"
print(classroom1)

[["Martha", "Alex"], 
 ["Max", "Anahi"], 
 ["Available", "Available"], 
 ["Alexis", "Rigel"]]

But I still can't get an idea of how to solve it according to the problem. I don't know how to solve it.

CodePudding user response：

Would this be what you're looking for?

classroom1[-1,-2] = "Alex"
print(classroom1)

Output:

[['Martha' 'Available']
 ['Max' 'Anahi']
 ['Available' 'Available']
 ['Alex' 'Rigel']]

CodePudding user response：

We can use reverse indexing or negative indexing to solve this problem. With positive/normal indexing you traverse through an array start through end. But with reverse indexing you use "-" sign with indexes and it traverses in the reverse direction.

consider this example:

x = np.array(['a','b','c','d','e','f','g'])
print(x[2])
print(x[-5])

so both these instructions will pring out 'c' one thing to remember is that in reverse indexing we start from -1 so if you want to print 'g' you would have to pass x[-1]

Now to your original problem: you have a 2 dimensional array that means you will have to pass two negative indexes to do the required modification

classroom[index of subarray][index of element within subarray]

consider another example:

classroom1[0,1] = "Alex"
print(classroom1)
[["Martha", "Alex"], 
 ["Max", "Anahi"], 
 ["Available", "Available"], 
 ["Alexis", "Rigel"]]

say we want to update the seat at index 0 in array at index 2, so we will have to do reverse indexing as follows:

classroom[-2][-2] = "Peter"
[["Martha", "Alex"], 
 ["Max", "Anahi"], 
 ["Peter", "Available"], 
 ["Alexis", "Rigel"]]

CodePudding user response：

Code:-

import numpy as np

classroom1 = np.array([["Martha", "Available"], 
                       ["Max", "Anahi"], 
                       ["Available", "Available"], 
                       ["Alexis", "Rigel"]])
list_of_names=['Yash','Sam','Itachi','Ace']

seats_available=0
for i in range(len(classroom1)):
    for j in range(len(classroom1[0])):
        if classroom1[i][j]=="Available":
            seats_available =1
#Enter the students in order right to left and starting from the last
count=0
for i in range(len(classroom1)-1,-1,-1):
    for j in range(len(classroom1[0])-1,-1,-1):
        if classroom1[i][j]=="Available":
            if seats_available and count<len(list_of_names):
                classroom1[i][j]=list_of_names[count]
                count =1
                seats_available-=1
print(classroom1)  #as you can see Ace is not present cause there is no available seats for them when he appeared.

Output:-

[['Martha' 'Itachi']
 ['Max' 'Anahi']
 ['Sam' 'Yash']
 ['Alexis' 'Rigel']]