Multiple Conditions

Quick reference

• 00:05 Okay, in the last video we looked at how to select data based on conditional
• 00:08 statements.
• 00:09 In this video, we want to look at multiple conditional statements.
• 00:12 So more than one condition.
• 00:15 So if you were confused in the last video,
• 00:17 you're going to have your mind blown in this one.
• 00:19 Okay, so here's our conditional from our last video.
• 00:21 So we're just looking for any rows with totals less than 0.
• 00:26 And when we run this, we get two rows.
• 00:29 Because in our original data frame here,
• 00:31 these are the only two rows that have less than 0 things.
• 00:35 Well, what if we wanted to search for more than just that one conditional.
• 00:39 How would we do that.
• 00:40 Well, we can use and and or.
• 00:42 And to do that, all we have to do is wrap our conditional statement in parentheses,
• 00:48 and then use, and or or, and then just create another conditional statement.
• 00:52 Now, this won't exactly work, we're going to get an error if we do this, and
• 00:56 I'll show you why in just a second.
• 00:57 But this is basically the logic behind it.
• 00:59 So let's create a second conditional statement.
• 01:02 I'm just going to copy this whole thing here and paste it in.
• 01:07 So we want totals less than 0, and
• 01:11 let's search for Wednesday's less than -1.
• 01:16 So, this is -0.2, that's not less than -1.
• 01:22 This is -1.9, that is less than -1.
• 01:26 So we should just get this row, C.
• 01:30 So let's shift enter to run this.
• 01:32 And we get that error that I was talking about,
• 01:34 truth value of a series is ambiguous.
• 01:36 And that's because we can't actually use the word and.
• 01:40 Now, with Python, regular Python,
• 01:42 when you're doing multiple conditional statements,
• 01:44 you could just use the word and, and it works, but it doesn't for pandas.
• 01:47 And the reason that is is because we're talking about lots of
• 01:50 different numbers here.
• 01:52 And pandas has a hard time evaluating lots of different numbers with the and
• 01:56 function, right.
• 01:57 So instead of using and, we have to use the ampersand.
• 02:01 It's just this guy right here.
• 02:02 And that's usually shift seven on most keyboards.
• 02:05 And a lot of programming languages, they use either and or the ampersand,
• 02:10 or in some cases, they use both.
• 02:11 So this is not such a weird thing.
• 02:13 It's just what pandas requires.
• 02:15 So now if we go ahead and run this,
• 02:17 we get in fact C, which is the column we thought we would get.
• 02:20 Because we're here, our total is less than 0.
• 02:23 Well, here total is less than 0, and Wednesday is less than -1.
• 02:30 Wednesday is less than -1.
• 02:31 No other rows in our data frame meet this condition, right.
• 02:36 So in order for this to evaluate true, this and this both have to be true.
• 02:44 If either one of those isn't true, the whole thing won't evaluate into true, and
• 02:48 that's why none of these other rows got selected, because it wasn't true for
• 02:51 those rows.
• 02:52 So that's and.
• 02:54 Now we can also use or, o r.
• 02:57 But just like with and, if we try and run this with or,
• 02:59 we're going to get that same truth value series is ambiguous error.
• 03:03 And so for or, we need to use the symbol for or, which is the pipe,
• 03:07 which is that straight bar, up and down, right.
• 03:10 So if we run this, we get a bunch of results, A, B, and C because here,
• 03:16 either one of these has to be true in order for this to evaluate true, right.
• 03:21 So this has to be true or this has to be true.
• 03:26 One or the other, or they can both be.
• 03:29 So let's look at this.
• 03:30 Total's less than 0.
• 03:32 Well, that's this one, this one, and this one, B, C, and D, right.
• 03:37 Well, D's not here, and A is here.
• 03:39 So what's going on.
• 03:40 Well, let's keep looking at this.
• 03:42 We also want or, so let's see.
• 03:46 So B and C are both negative.
• 03:48 So B and C shows up, but A is positive.
• 03:53 Well, we also want to search for Wednesday less than -1.
• 03:57 So, for A, it's Wednesday is less than -1 just barely, by 0.04, right.
• 04:04 So A gets put on here, because or evaluated true for A.
• 04:09 Even though this was false, this was true.
• 04:13 And since only one of these two have to be true, A gets added.
• 04:16 So those are multiple conditionals.
• 04:19 So just remember you can't use the words and and or,
• 04:22 you have to use the ampersand or the pipe symbol.
• 04:25 And other than that, it's pretty simple.
• 04:28 You just hash your conditional statements in your parentheses and you're good to go.
• 04:32 So, in the next video, we'll go ahead and look at changing indexes.

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