MORE ON FUNCTIONS: ARGUMENTS, CREATING, PRINTING, SAVING RESULTS, RETURNING RESULTS
Introduction—-
Whether your dealing with data types, reading in data, or other analytic tasks
a fundamental principle of data analytic languages, and programming in
general, is to avoid repeating code. This concept is often abbreviated as DRY:
Don’t repeat yourself. One reason why you should not repeat code is because
it’s a waste of time. Repeating code also leads to more lines of code to
The opposite of DRY code is WET code in which you write out the process every
time.
One way to avoid using WET code is to package a process or routine into a
function. In this lesson I assume that you’ve already had some experience using
functions in R. So, I want to dive deeper into functions so that you can use
them more effectively. I think a great way to learn about functions is to
create some yourself.
about how to use and create them.
Arguments to functions—-
Also known as parameters. With respect to a function, they are the variables.
The process performed by the function will not change, but the output will
change based on the arguments.
?log # In the help, there are two arguments: x, and base. The = exp(1) after the base means that there's a default value that will be used if you don't assign it a value.## starting httpd help server ... donelog(x = 100, base = 10) # You can explicitly identify the values for each argument## [1] 2log(100, 10) # But you don't have to if they come in the order that the arguments are taken## [1] 2log(base = 10, x = 100) # You can put them out of order if you explictly identify them## [1] 2?sum # In the help, there are two arguments: ..., and na.rm. The ellipsis ... means that the number of arguments can vary
sum(1,3,5)## [1] 9Creating functions—-
Let’s create a function that uses the built-in cars dataset
?cars
summarizeAndPlot <- function(dataframe = cars, column = 'speed'){
summary(dataframe)
paste0('The value in row 1, column 1 is: ', dataframe[1,1])
paste0('The value in row 2, column 2 is: ', dataframe[2,2])
hist(dataframe[,column])
}
summarizeAndPlot() # Notice that it prints the histogram, but not the summary stats or other lines of text. It will only print text if it comes last.
# Printing—- # Give instructions to print the summary statistics
summarizeAndPlot <- function(dataframe = cars, column = 'speed'){
print(summary(dataframe))
print(paste0('The value in row 1, column 1 is: ', dataframe[1,1]))
print(paste0('The value in row 2, column 2 is: ', dataframe[2,2]))
hist(dataframe[,column])
}
summarizeAndPlot() # This now prints the summary statistics and the other two lines of text.## speed dist
## Min. : 4.0 Min. : 2.00
## 1st Qu.:12.0 1st Qu.: 26.00
## Median :15.0 Median : 36.00
## Mean :15.4 Mean : 42.98
## 3rd Qu.:19.0 3rd Qu.: 56.00
## Max. :25.0 Max. :120.00
## [1] "The value in row 1, column 1 is: 4"
## [1] "The value in row 2, column 2 is: 10"
# Let’s test it out on another dataset
j17i <- read.csv('jan17Items.csv', sep = ',') # Read in the jan17Items.csv dataset
summarizeAndPlot(j17i, 'Tax') # It works well!## Time OperationType BarCode CashierName
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## LineItem Department Category CardholderName
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## RegisterName StoreNumber TransactionNumber CustomerCode
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## Cost Price Quantity Modifiers
## Min. :-189.0400 Min. :-322.810 Min. : 1.000 Min. :-2.5200
## 1st Qu.: 0.1100 1st Qu.: 4.500 1st Qu.: 1.000 1st Qu.: 0.0100
## Median : 0.1100 Median : 12.020 Median : 1.000 Median : 0.0100
## Mean : 0.2108 Mean : 9.612 Mean : 1.177 Mean : 0.6548
## 3rd Qu.: 0.1100 3rd Qu.: 14.680 3rd Qu.: 1.000 3rd Qu.: 1.0800
## Max. : 189.0300 Max. : 24.630 Max. :36.000 Max. :57.5500
## NA's :562
## Subtotal Discounts NetTotal Tax
## Min. :-322.80 Min. : -0.0300 Min. :-322.77 Min. :-25.340
## 1st Qu.: 5.24 1st Qu.: -0.0300 1st Qu.: 4.87 1st Qu.: 0.410
## Median : 13.10 Median : -0.0300 Median : 13.13 Median : 1.040
## Mean : 15.10 Mean : 0.7626 Mean : 14.34 Mean : 1.131
## 3rd Qu.: 15.76 3rd Qu.: -0.0300 3rd Qu.: 15.79 3rd Qu.: 1.230
## Max. :3328.12 Max. :951.8300 Max. :3328.15 Max. :261.260
## NA's :341
## TotalDue
## Min. :-348.11
## 1st Qu.: 5.68
## Median : 14.17
## Mean : 15.88
## 3rd Qu.: 17.02
## Max. :3589.41
## NA's :341
## [1] "The value in row 1, column 1 is: 2017-01-26T21:18:00Z"
## [1] "The value in row 2, column 2 is: SALE"
# Saving results—- # Modify the function to return the summary
statistics. # You can save whatever is returned from a function into an
object
a # This returns the contents of the variable a to the console. Notice that it creates a list that has elements needed for the histogram, but not the summary statistics.
a <- summarizeAndPlot(j17i, 'Tax') # This runs the function and saves the returned values to the variable, a## Time OperationType BarCode CashierName
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## LineItem Department Category CardholderName
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## RegisterName StoreNumber TransactionNumber CustomerCode
## Length:8899 Length:8899 Length:8899 Length:8899
## Class :character Class :character Class :character Class :character
## Mode :character Mode :character Mode :character Mode :character
##
##
##
##
## Cost Price Quantity Modifiers
## Min. :-189.0400 Min. :-322.810 Min. : 1.000 Min. :-2.5200
## 1st Qu.: 0.1100 1st Qu.: 4.500 1st Qu.: 1.000 1st Qu.: 0.0100
## Median : 0.1100 Median : 12.020 Median : 1.000 Median : 0.0100
## Mean : 0.2108 Mean : 9.612 Mean : 1.177 Mean : 0.6548
## 3rd Qu.: 0.1100 3rd Qu.: 14.680 3rd Qu.: 1.000 3rd Qu.: 1.0800
## Max. : 189.0300 Max. : 24.630 Max. :36.000 Max. :57.5500
## NA's :562
## Subtotal Discounts NetTotal Tax
## Min. :-322.80 Min. : -0.0300 Min. :-322.77 Min. :-25.340
## 1st Qu.: 5.24 1st Qu.: -0.0300 1st Qu.: 4.87 1st Qu.: 0.410
## Median : 13.10 Median : -0.0300 Median : 13.13 Median : 1.040
## Mean : 15.10 Mean : 0.7626 Mean : 14.34 Mean : 1.131
## 3rd Qu.: 15.76 3rd Qu.: -0.0300 3rd Qu.: 15.79 3rd Qu.: 1.230
## Max. :3328.12 Max. :951.8300 Max. :3328.15 Max. :261.260
## NA's :341
## TotalDue
## Min. :-348.11
## 1st Qu.: 5.68
## Median : 14.17
## Mean : 15.88
## 3rd Qu.: 17.02
## Max. :3589.41
## NA's :341
## [1] "The value in row 1, column 1 is: 2017-01-26T21:18:00Z"
## [1] "The value in row 2, column 2 is: SALE"
a## $breaks
## [1] -40 -20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
##
## $counts
## [1] 2 19 8520 11 3 1 0 0 1 0 0 0 0 0 0
## [16] 1
##
## $density
## [1] 1.168497e-05 1.110072e-04 4.977799e-02 6.426735e-05 1.752746e-05
## [6] 5.842487e-06 0.000000e+00 0.000000e+00 5.842487e-06 0.000000e+00
## [11] 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00
## [16] 5.842487e-06
##
## $mids
## [1] -30 -10 10 30 50 70 90 110 130 150 170 190 210 230 250 270
##
## $xname
## [1] "dataframe[, column]"
##
## $equidist
## [1] TRUE
##
## attr(,"class")
## [1] "histogram"Returning—-
Adjust the function so that it returns the summary statistics
summarizeAndPlot <- function(dataframe = cars, column = ‘speed’){ print(summary(dataframe)) return(summary(dataframe)) # This is the line of code that returns the summary statistics hist(dataframe[,column]) } a <- summarizeAndPlot(j17i, ‘Tax’) # Now run the function and save the returned output to variable a again. a # You can see that the summary statistics are now the contents of a