Subsetting and sorting

Jeffrey Leek
Johns Hopkins Bloomberg School of Public Health

Subsetting - quick review

set.seed(13435)
X <- data.frame("var1"=sample(1:5),"var2"=sample(6:10),"var3"=sample(11:15))
X <- X[sample(1:5),]; X$var2[c(1,3)] = NA
X

  var1 var2 var3
1    2   NA   15
4    1   10   11
2    3   NA   12
3    5    6   14
5    4    9   13

Subsetting - quick review

X[,1]

[1] 2 1 3 5 4

X[,"var1"]

[1] 2 1 3 5 4

X[1:2,"var2"]

[1] NA 10

Logicals ands and ors

X[(X$var1 <= 3 & X$var3 > 11),]

  var1 var2 var3
1    2   NA   15
2    3   NA   12

X[(X$var1 <= 3 | X$var3 > 15),]

  var1 var2 var3
1    2   NA   15
4    1   10   11
2    3   NA   12

Dealing with missing values

X[which(X$var2 > 8),]

  var1 var2 var3
4    1   10   11
5    4    9   13

Sorting

sort(X$var1)

[1] 1 2 3 4 5

sort(X$var1,decreasing=TRUE)

[1] 5 4 3 2 1

sort(X$var2,na.last=TRUE)

[1]  6  9 10 NA NA

Ordering

X[order(X$var1),]

  var1 var2 var3
4    1   10   11
1    2   NA   15
2    3   NA   12
5    4    9   13
3    5    6   14

Ordering

X[order(X$var1,X$var3),]

  var1 var2 var3
4    1   10   11
1    2   NA   15
2    3   NA   12
5    4    9   13
3    5    6   14

Ordering with plyr

library(plyr)
arrange(X,var1)

  var1 var2 var3
1    1   10   11
2    2   NA   15
3    3   NA   12
4    4    9   13
5    5    6   14

arrange(X,desc(var1))

  var1 var2 var3
1    5    6   14
2    4    9   13
3    3   NA   12
4    2   NA   15
5    1   10   11

Adding rows and columns

X$var4 <- rnorm(5)
X

  var1 var2 var3     var4
1    2   NA   15  0.18760
4    1   10   11  1.78698
2    3   NA   12  0.49669
3    5    6   14  0.06318
5    4    9   13 -0.53613

Adding rows and columns

Y <- cbind(X,rnorm(5))
Y

  var1 var2 var3     var4 rnorm(5)
1    2   NA   15  0.18760  0.62578
4    1   10   11  1.78698 -2.45084
2    3   NA   12  0.49669  0.08909
3    5    6   14  0.06318  0.47839
5    4    9   13 -0.53613  1.00053

Notes and further resources