Presentation on demonstrating function "factor" in R
Ashu Guru
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03/07/2019
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Presentation on demonstrating function "factor" in R
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- [00:00:00.320]We will now take a look at the function which is called factor.
- [00:00:05.440]In order to understand what factor helps us do,
- [00:00:09.013]let's first look at the file that contains our data.
- [00:00:12.960]So assume that we have a file which has first row as the column headers for a
- [00:00:22.434]table and there are 5 columns plot, entry name, block,
- [00:00:29.114]TSW and we have 9 rows of data.
- [00:00:33.520]Another thing to notice is that even though that the scientist has used
- [00:00:40.402]numbers to represent plots, they are actually categorical variables
- [00:00:46.903]or what should be treated as factors.
- [00:00:52.160]Similarly, the entries are categorical variables.
- [00:00:58.920]That means they actually represent levels of a factor rather than a numeric value,
- [00:01:05.417]even though we are using a numeric ID to represent them.
- [00:01:10.200]The name give us a indication that it is actually a categorical variable because
- [00:01:15.480]two of the values in that column are string literals.
- [00:01:20.720]And again, consider that block for the experiment is
- [00:01:25.270]actually another categorical variable, but the scientist chose to use an ID or a
- [00:01:32.225]number to represent it.
- [00:01:35.440]Now when we read this table in R, by default R we'll be able to understand
- [00:01:41.440]the name is actually a categorical variable because it finds that few of the
- [00:01:47.600]values in that column are string literal, so it understands.
- [00:01:52.480]I'm going to treat this as a factor variable with different levels.
- [00:01:58.080]However, for our to implicitly treat plot entry
- [00:02:02.620]and block is not possible.
- [00:02:05.360]So somehow we will have to force our to think to treat plot name and plot entry
- [00:02:11.013]and block also as categorical variables.
- [00:02:13.840]And this is done using factor function.
- [00:02:17.040]So let's take a look.
- [00:02:19.480]So as a first step I'm going to change the working directory of the of R to the
- [00:02:25.141]folder where I have my text file or my CSV file with the data.
- [00:02:30.280]So I'm going to run the set WD command and now I will load the file which is
- [00:02:39.496]testdata. CSV in a variable called field data table.
- [00:02:51.600]Let's see the structure of this new variable that we created.
- [00:02:56.360]As I mentioned earlier that R was able to identify name as a factor variable.
- [00:03:02.960]However, plot is still integer, entry is still integer and block is still
- [00:03:09.962]integer.
- [00:03:10.720]However, in our experiment the scientist has just
- [00:03:14.454]used numbers to represent these categorical values but the variable
- [00:03:19.532]itself is actually a factor or a categorical variable.
- [00:03:23.640]So now we are going to use a function called factor.
- [00:03:27.160]And what it basically says is that in this table variable,
- [00:03:35.464]the column value plot treat this as factor where the values come from the
- [00:03:45.881]field same tables column.
- [00:03:51.520]And I'm going to run the same command for entry and block as well.
- [00:03:58.360]And finally I'm going to print the structure of the variable field data
- [00:04:03.880]table again.
- [00:04:04.800]So now if we compare the previous print out to the new print out,
- [00:04:10.271]we can see that now R understands that plot must be treated as a factor,
- [00:04:16.323]entry must be treated as a factor, block must be treated as factor,
- [00:04:21.961]which is unlike the initial readout which said plot and entry was integer and block
- [00:04:28.925]was integer.
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