Removing elements from a list

### 6.3.8 Removing elements from a list

Elements can be removed from a list by using either the suppress command (which removes a single element) or the remove command (which removes all elements meeting a given conditions).

- suppress takes two arguments:
  - L, a list.
  - i, a nonnegative integer.
- suppress(L,i) returns the list L with the element at index i removed.
- remove takes two arguments:
  - f, a boolean function.
  - L, a list.
- remove(f,L) returns the sublist of L with the elements c such that f(c)==true removed.

#### Examples

suppress([3,4,2],1)

| ⎡ ⎣ | 3,2 | ⎤ ⎦

remove(x->(x>=2),[0,1,2,3,1,5])

| ⎡ ⎣ | 0,1,1 | ⎤ ⎦

You can use remove to remove characters from a string. For example, to remove all instances of a given letter from a string, enter the following code in a program editor level (see Section 25.1.2 for writing functions):

f(s,c):={ local ordc,l,r,x,k; ordc:=ord(c); l:=length(s)-1; purge(x,k); r:=remove(x->(ord(x)==ordc),seq(s[k],k,0,l)); return char(ord(r)); }

Here s is the input string an c is the letter to be removed. Now, for example:

f("abracadabra","a")

“brcdbr” |  |  |  |  |  |  |  |  |  |