Using an If loop in Mathematica

[Physicslad78]

Dear all,

I have a list of pairs say Li={{a,x},{b,y},{c,z}...}. I want to eliminate from this list all pairs that have their second part i.e the x, y, z...>1 and I was thing of using an If loop. Can anyone tell me how please...



Thanks...

 

[bcbwilla]

There is probably a more elegant way of doing it (it wouldn't surprise me if Mathematica has some built in function for this), but this should get you started:

L2 = {};
Do[
    If[Li[[i, 2]] <= 1, AppendTo[L2, Li[[i]]]]
    ,{i, Length[Li]}]
L1 = L2;

 

[diana amir]

question : For each number k from 1 to 10, print half the number if k is even and twice the number if k is odd.
<I think this question involving loop but i ddnt how to solve it. anyone ?>

 

[Bill Simpson]

(*One built in function to eliminate pairs matching a condition using pattern matching*)

In[1]:= v={{1,7},{2,-5},{3,0},{4,9}};DeleteCases[v,{x_,y_/;y>1}]
Out[2]= {{2,-5},{3,0}}

(*one method of printing using a For*)

In[3]:= For[k=1,k≤10,k++,
If[EvenQ[k],Print[k/2],Print[2k]]
]

From In[3]:= 2
From In[3]:= 1
From In[3]:= 6
From In[3]:= 2
From In[3]:= 10
From In[3]:= 3
From In[3]:= 14
From In[3]:= 4
From In[3]:= 18
From In[3]:= 5

(*another method using pattern matching*)

In[4]:= k=.; (*clear that value assigned to k*)
Range[10]/.{k_/;EvenQ[k]->k/2,k_/;OddQ[k]->2k}

Out[5]= {2,1,6,2,10,3,14,4,18,5}

 

[alphy]

Hello there,

Using an If loop in Mathematica is a great way to eliminate specific elements from a list. In this case, you can use the Select function to achieve your goal. Here's an example of how you can do it:

Li = {{a,x},{b,y},{c,z}...}

newLi = Select[Li, #[[2]] <= 1 &]

This code will create a new list called newLi that only contains pairs where the second element is less than or equal to 1. You can modify the condition inside the Select function to fit your specific needs. I hope this helps! Let me know if you have any further questions.