Q about Lesson 4 Demo: Using Expressions to Create New Columns

[AJS1]

Is StormType="Tropical Storm; necessary to create the new column MaxWindKM?  If not, what information is StormType pulling from to make the new column Tropical Storm?

data tropical_storm;

set pg1.storm_summary;

drop Hem_EW HEM_NS Lat Lon;

where Type="TS";

MaxWindKM=MaxWindMPH*1.60934;

format MaxWindKM 3.;

StormType="Tropical Storm";

run;

[Reeza]

Is StormType="Tropical Storm; necessary to create the new column MaxWindKM? 

No, they are independent statements.

If not, what information is StormType pulling from to make the new column Tropical Storm?

No information is being 'pulled' it's what you can a manual coding or hard coded value. 

I'm assuming someone is creating a label that will make sense when the file is combined with other files to indicate the other storm types. 

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@AJS1 wrote:

Is StormType="Tropical Storm; necessary to create the new column MaxWindKM?  If not, what information is StormType pulling from to make the new column Tropical Storm?

data tropical_storm;

set pg1.storm_summary;

drop Hem_EW HEM_NS Lat Lon;

where Type="TS";

MaxWindKM=MaxWindMPH*1.60934;

format MaxWindKM 3.;

StormType="Tropical Storm";

run;

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[Panagiotis · Accepted solution]

Hi @AJS1 ,

Let me see if I understand your question correct. You are asking if the statement StormType="Tropical Storm"; is required to create the new column MaxWindKM?

The answer is no, it's not necessary. The StormType='Tropical Storm' creates another column that essentially explains what the Type column means. If you look at the Type column you will see a TS. TS is an abbreviation, so you decided to add another column that explains TS (or Tropical Storm).

One way to check is to break everything down and test it. First I suggestion run the DATA step without the StormType='Tropical Storm' and see what happens. In this example I commented out StormType='Tropical Storm'.

data tropical_storm;
  set pg1.storm_summary;
  drop Hem_EW HEM_NS Lat Lon;
  where Type="TS";
  MaxWindKM=MaxWindMPH*1.60934;
  format MaxWindKM 3.;
  *StormType="Tropical Storm";
run;

Results:

You can see that the MaxWindKM was still created from the assignment statement in yourcode (MaxWindKM=MaxWindMPH*1.60934). However you don't have the StormType column. 

So let's add back in StormType='Tropical Storm' and see our results.

data tropical_storm;
  set pg1.storm_summary;
  drop Hem_EW HEM_NS Lat Lon;
  where Type="TS";
  MaxWindKM=MaxWindMPH*1.60934;
  format MaxWindKM 3.;
  StormType="Tropical Storm";
run;

Results:

All you are doing with those assignment statements is creating a new column. In the case of the MaxWindKM you are creating a new column based on a calculation for each row. The new StormType column is being created with a static string. Try adding another column or two and see the different results.

Hope this helps. Please let me know if you have any other questions.

- Peter

[AJS1]

How does the program know that TS is the same as Tropical Storm?  

Thank you.

[Tom]

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@AJS1 wrote:

How does the program know that TS is the same as Tropical Storm?  

Thank you.

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The program does not know that.  The programmer knew that and so that is why they wrote the program in this way.

[Panagiotis]

When you wrote StormType='Tropical Storm' you told it. The program only knows that because of you, the programmer.

For fun, change 'Tropical Storm' to any other string. Just put your name in it for instance. When you run the program you will now have a column full of your name as the value. Now obviously that is not correct when analyzing storm data, but hopefully you see what you are doing. 

In this specific demo, we are telling you to do it. When working with real world data at work you will have to know about your data, and what abbreviations mean.

Hope that helped.

- Peter