How to rename variables in R

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When we have created a data frame in R , for example by reading a csv file from working directory, the first row of the file will be used as the column or variable names of the data frame. Then we can use names() function to rename the variable names as we like. In the following example, a data frame ‘ grade’ is created by reading a csv file from the current working directory, then the variable for test data is renamed as ‘testDate’.

#set the column variable type, then read csv file into a data frame
vartype<-c("character", "character", "character", "character", "character", "numeric","numeric", "numeric","numeric","character")
grade <- read.table("University-NA.csv", colClasses=vartype, header=TRUE, sep=",")                                      
#show the data frame structure
str(grade)
#output
'data.frame':	20 obs. of  10 variables:
 $ StudentID: chr  "1" "2" "3" "4" ...
 $ First    : chr  "James" "Wilson" "Richard" "Mary" ...
 $ Last     : chr  "Zhang" "Li" "Nuan Ye" "Deng" ...
 $ Gender   : chr  "Male" "Male" "Male" "Female" ...
 $ Country  : chr  "US" "UK" "UK" "US" ...
 $ Age      : num  23 26 35 21 19 43 37 28 19 25 ...
 $ Math     : num  73 95 77 60 77 79 87 95 73 66 ...
 $ Physics  : num  70 999 83 99 89 64 99 87 92 93 ...
 $ Chemistry: num  87 83 92 84 93 83 67 93 84 999 ...
 $ Date     : chr  "10/31/08" "03/16/08" "05/22/08" "01/24/09" ...

#to show current variable names
names(grade)  
#output
[1] "StudentID" "First"     "Last"      "Gender"    "Country"  
 [6] "Age"       "Math"      "Physics"   "Chemistry" "Date"     
#set new name for 10th column, Date variable
names(grade)[10] <- "testDate"      
#show column names again
names(grade)
#output
[1] "StudentID" "First"     "Last"      "Gender"    "Country"  
 [6] "Age"       "Math"      "Physics"   "Chemistry" "testDate" 

#to show first 3 observations
head(grade,3)
#output
StudentID   First    Last Gender Country Age Math Physics
1         1   James   Zhang   Male      US  23   73      70
2         2  Wilson      Li   Male      UK  26   95     999
3         3 Richard Nuan Ye   Male      UK  35   77      83
  Chemistry testDate
1        87 10/31/08
2        83 03/16/08
3        92 05/22/08

Package ‘plyr’ provides a function rename(), which can just input the old and new value of the column when renaming variables. In the following code example, we rename the columns for Physics and Chemistry of data frame ‘grade’.

# Renaming columns 'Physics' and 'Chemistry'
grade <- rename(grade, c("Physics"="Phy", "Chemistry"="Chem")) 
#show data frame first 3 observations
head(grade,3)
#output
  StudentID   First    Last Gender Country Age Math Phy Chem
1         1   James   Zhang   Male      US  23   73  70   87
2         2  Wilson      Li   Male      UK  26   95 999   83
3         3 Richard Nuan Ye   Male      UK  35   77  83   92
  testDate
1 10/31/08
2 03/16/08
3 05/22/08

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