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Alright, so let's talk about safely
removing values from a list. Alright, so

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we've seen how not to remove outlying
values from an ordered set of data, in

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the last video. Now let's have a look
at something that will work. Note that I

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said ordered data there. We'll see how to
delete items from an unsorted list next.

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This code will only work when the data
is sorted. I'm going to delete the

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commented out code, and all the code that
didn't work from the last video, first.

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Okay, so I'm going to assume that we
don't have enough memory to copy the list.

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I know our list is quite small but you
might be working with gigabytes of data

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in some scenarios. In that case, you may
not have enough RAM for copying the

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entire list. So what we're going to do is
start off by stripping off the low

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values from the start of the list. So
let's write some code for that.

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So line 7, I'm going to put a comment
here to tell us what we're doing:

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process the low values in the list.

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And we'll start coding. You want to make stop
equals zero, line 9, for index comma value

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in enumerate with data in
parentheses, colon, and we're gonna type

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if value is greater than equal to min_valid : stop equals index, break.

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Then moving on down, line 14, I'm
going to type print stop - that's for

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debugging purposes -
come back and over that, and del data,

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left square bracket, colon stop, right square
bracket and print data.

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Okay, so there's our code. So the approach is pretty straightforward

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We initialize stop to zero on line eight.
On line 15 we delete the slice from the

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beginning of the list, up to, but not
including, stop. Inside the loop we keep

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incrementing the stop value, until we find
a value that shouldn't be deleted. Remember

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that a slice extends up to, but not
including, the stop value. That means the

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value we've stopped out won't be deleted.
So let's run the program. As you can see,

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the first two values have been removed.
Stop has the value 2, as you can see

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from the output, and line 15 deleted the
slice from the start of the list, up to,

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but not including the value at position
2. The important thing here is that we

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don't change the data inside the loop.
It's only after the loop terminates, that

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we delete the slice from data. Alright, so
in the next video, we'll remove the high

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outlying values - that's the values 350
and 360 from the end of the list.

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See you in the next video.