PDB_Stat_100_Lecture_06

PDB_Stat_100_Lecture_06 - STA 100 Lecture 6 Paul Baines...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
STA 100 Lecture 6 Paul Baines Department of Statistics University of California, Davis January 14th, 2011
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Admin for the Day I Homework 2 posted, due Wednesday, Jan 19th in class I NO CLASS MONDAY – MLK DAY! I Comments: In the math and statistics world, log always means natural log i.e., log e or ‘ln’ as you may have seen previously. e.g., log(animals $ body) will give the (natural) log brain weights. ( ln doesn’t exist in R ).
Background image of page 2
Admin for the Day I Homework 2 posted, due Wednesday, Jan 19th in class I NO CLASS MONDAY – MLK DAY! I Comments: In the math and statistics world, log always means natural log i.e., log e or ‘ln’ as you may have seen previously. e.g., log(animals $ body) will give the (natural) log brain weights. ( ln doesn’t exist in R ). References for Today: Rosner, Ch 3.7-3.8 (7th Ed.) References for Wednesday: Rosner, Ch 4.1-4.9 (7th Ed.)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Some R Tips/Tricks You need two things to complete the R portion on Hwk 2: sampling and subsetting .
Background image of page 4
Some R Tips/Tricks You need two things to complete the R portion on Hwk 2: sampling and subsetting . I Subsetting Data: Point-and-click via: Data > Active Dataset > Subset active dataset Choose a logical (T/F) subset expression . For example: animal == "Cow" Give your subset a different name! Note the double == .
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Subsetting Data by Hand I Manually Subsetting Data: Simple examples: > animals[1,] # show the first row > animals[1:5,] # Show the first 5 rows > animals[,"brain"] # show the "brain" column A more sophisticated example: > # Pick only those animals whose body size > # is bigger than the median body size > x.med <- median(animals$body) > subby <- animals[animals$body > x.med, ] > subby animal body brain 2 Cow 465.0 423.0 6 Dipliodocus 11700.0 50.0 ...etc. ..
Background image of page 6
Random Samples in R I Sampling in R : You can sample from a list of values in R using the sample function: > x <- c(1:10) # x = (1,2,3,4,5,6,7,8,9,10) > # Randomly pick 4 values from x > first.one <- sample(x,4) > second.time <- sample(x,4) # do it again. .. > first.time [1] 3 6 1 4 > second.time [1] 1 2 3 8 > animals[first.time,] animal body brain 3 Grey wolf 36.33 119.5 6 Dipliodocus 11700.00 50.0 1 Mountain beaver 1.35 465.0 4 Goat 27.66 115.0
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Putting it together I We can now randomly pick which rows to keep, and we know how to pick out a subset of rows. Together: > # Randomly pick 4 of the 27 animals > animals[sample(1:27,4),] animal body brain 17 Rhesus monkey 6.8 179 23 Jaguar 100.0 157 2 Cow 465.0 423 15 African elephant 6654.0 5712
Background image of page 8
Putting it together I We can now randomly pick which rows to keep, and we know how to pick out a subset of rows. Together: > # Randomly pick 4 of the 27 animals > animals[sample(1:27,4),] animal body brain 17 Rhesus monkey 6.8 179 23 Jaguar 100.0 157 2 Cow 465.0 423 15 African elephant 6654.0 5712 You will get a different answer each time! ,
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Recall: I SRS: Everyone has same chance of being picked. I
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/09/2011 for the course STAT 100 taught by Professor drake during the Spring '10 term at UC Davis.

Page1 / 73

PDB_Stat_100_Lecture_06 - STA 100 Lecture 6 Paul Baines...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online