R for loop skip to next iteration ifelse

for-loopr

Suppose you have a for loop like so

for(n in 1:5) {
  #if(n=3) # skip 3rd iteration and go to next iteration
  cat(n)
}

How would one skip to the next iteration if a certain condition is met?

Best Answer

for(n in 1:5) {
  if(n==3) next # skip 3rd iteration and go to next iteration
  cat(n)
}

Related Solutions

Java – way to access an iteration-counter in Java’s for-each loop

No, but you can provide your own counter.

The reason for this is that the for-each loop internally does not have a counter; it is based on the Iterable interface, i.e. it uses an Iterator to loop through the "collection" - which may not be a collection at all, and may in fact be something not at all based on indexes (such as a linked list).

Javascript – Why is using “for…in” for array iteration a bad idea

The reason is that one construct:

var a = []; // Create a new empty array.
a[5] = 5;   // Perfectly legal JavaScript that resizes the array.

for (var i = 0; i < a.length; i++) {
    // Iterate over numeric indexes from 0 to 5, as everyone expects.
    console.log(a[i]);
}

/* Will display:
   undefined
   undefined
   undefined
   undefined
   undefined
   5
*/

can sometimes be totally different from the other:

var a = [];
a[5] = 5;
for (var x in a) {
    // Shows only the explicitly set index of "5", and ignores 0-4
    console.log(x);
}

/* Will display:
   5
*/

Also consider that JavaScript libraries might do things like this, which will affect any array you create:

// Somewhere deep in your JavaScript library...
Array.prototype.foo = 1;

// Now you have no idea what the below code will do.
var a = [1, 2, 3, 4, 5];
for (var x in a){
    // Now foo is a part of EVERY array and 
    // will show up here as a value of 'x'.
    console.log(x);
}

/* Will display:
   0
   1
   2
   3
   4
   foo
*/

Best Answer

Related Solutions

Java – way to access an iteration-counter in Java’s for-each loop

Javascript – Why is using “for…in” for array iteration a bad idea

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