R:

1. Selecting observations by indexs

a. print all rows

   print(mydata[ ]) ; 
   print(mydata[, ]); 
   print(mydata[1:8])

b. Just observation 5:

print(mydata[5, ])

c. multiple

print(mydata[ c(5,6,7,8), ])

d. use indice

   myMindices <- c(5,6,7,8) ; 
   summary(mydata[myMindices, ])

e. print a list of index numbers for each observation

data.frame(myindex = 1:8, mydata)

f. Select data using length as the end

print(mydata[1:nrow(mydata), ])

2. By row names

a. Display row names

row.names (mydata)

print(mydata[ c("1", "2", "3", "4"), ])

b. Assign new names

mynames <- c("Ann", "Cary", "Sue") ; 
row.names(mydata) <- mynames 
print(mydata["Ann", ]) 
print(mydata [c("Ann", "Cary", "Sue", "Carla"), ]) 
myNames <- c("Ann", "Cary", "Sue"); 
print(mydata[mynames, ])

3. By logic

a.

myRows <- c(TRUE, TRUE, TRUE, TRUE, FALSE, FALSE, FALSE, FALSE) ;

print(mydata[myRows,])

b. select first four rows using 1 and 0:

myBinary <- c(1,1,1,1,0,0,0,0) ;

print(mydata[myBinary, ])

myRows <- as.logical(myBinary) ;

print(mydata\[myRows, ])

c.

print(mydata[mydata$gender == "f", ])

print(mydata[which(mydata$gender == "f"), ])

d. using a saved vector

myFemales <- which(mydata$gender == "f” ）

print(mydata[myFemales, ])

e. using %in%

myRsas <- which(mydata$workshop %in% c("R", "SAS"));

print(myRsas) ;

print(mydata[myRsas, ])

f. equvalent selections using different ways to refer to the variables

 print(subset(mydata, gender == 'f') )
  attach(mydata) 
  print(mydata[which(gender == 'f' ), ]) detach(mydata) 
  with(mydata, print(mydata[which(gender == 'f'), ])) 
  print(mydata[which(mydata['gender'] == "f"), ]) 
  print(mydata[which(mydata$gender =="f"), ])

4. By string search

search for row names that begin with “C”

myCindices <- grep("^C", row.names(mydata), value = FALSE) 

print(mydata[myCindices , ])

5. By subset function

subset(mydata, subset = gender == "f") 
summary( subset(mydata, subset = gender = "m" & q4 ==5) ）

6. Generating indices A to Z from two row names

myMaleA <- which(row.names(mydata) == "Bob") 
myMaleZ <- which(row.names(mydata) == "Rich") print(mydata[myMaleA :myMaleZ, ])

7. Creating a new data frame of selected observations

a. myMales <- mydata [5:8, ] 
b. myMales <- mydata[which(mydata$gender =="m"), ] 
c. myMales <- subset\(mydata, subset = gender == "m")

Selecting observations

R: