To find the mean of a column summarized by other column names and common values in those columns in data.table object in R, we can follow the below steps −First of all, create a data.table object.Then, melt the data.table object using melt function from reshape2 package.After that, use dcast function to find the mean of a column summarized by other column names and common values in those columns.ExampleCreate the data.table objectLet’s create a data.table object as shown below −library(data.table) ID

To find the total by year column in an R data frame, we can use aggregate function with sum function.For Example, if we have a data frame called df that contains a year colmn say Year and a numerical column say Demand then we can find the total Demand by Year with the help of command given below −aggregate(df["Demand"],by=df["Year"],sum)Example 1Following snippet creates a sample data frame −Year

To standardize selected columns in data.table object in R, we can follow the below steps −First of all, create a data.table object.Then, use scale function and cbind function with subsetting to standardize selected columns.ExampleCreate the data.table objectLet’s create a data.table object as shown below −library(data.table) var1

To repeat column values in R matrix by values in another column, we can follow the below steps −First of all, create a matrix.Then, use rep function along with cbind function to repeat column values in the matrix by values in another column.ExampleCreate the matrixLet’s create a matrix as shown below −x

To save a matrix as CSV file using R, we can use write.matrix function of MASS package. For Example, if we have a matrix called M and we want to save it as CSV file then we can use the below mentioned command −write.matrix(M,file="Mat.csv")ExampleFollowing snippet creates a sample matrix −M

To remove multiple columns from matrix in R by using their names, we can follow the below steps −First of all, create a matrix.Then, add names to columns of the matrix.After that, subset the matrix by deselecting the desired columns with negation and single square brackets for subsetting.ExampleCreate the matrixLet’s create a matrix as shown below −M

To find the index of values in R matrix column if they occur once, we can follow the below steps −First of all, create a matrix.Then, use which function along with duplicated function and single square brackets for subsetting to find the index of values in a column if they occur once.Example 1Create the data frameLet’s create a data frame as shown below −M1

To combine two columns by ignoring missing values if exists in one column in R data frame, we can use paste function and is.na function.For Example, if we have a data frame called df that contains two columns say C1 and C2 where C2 contains some missing values then we can use the below mentioned command to combine C1 and C2 by ignoring missing values in C2 −cbind(df,Combined=paste(df[,1],replace(df[,2],is.na(df[,2]),"")))Example 1Following snippet creates a sample data frame −x1

To find the common elements between two columns of an R data frame, we can use intersect function.For Example, if we have a data frame called df that contains two columns say X and Y then we can find the common elements between X and Y by using the below command −intersect(df$X,df$Y)Example 1Following snippet creates a sample data frame −x1

To subset an R data frame by specifying columns that contains NA, we can follow the below steps −First of all, create a data frame with some columns containing NAs.Then, use is.na along with subset function to subset the data frame by specifying columns that contains NA.ExampleCreate the data frameLet’s create a data frame as shown below −x