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To subset groups that occur less than n times in R data frame, we can use filter function of dplyr package.For Example, if we have a data frame called df that contains a grouping column say Group then we can subset groups that occur less than 4 times by using the below mentioned command −df%%group_by(Group)%%filter(n()=4)Example 1Following snippet creates a sample data frame −Grp
To find the sum of rows of a column based on multiple columns in R data frame, we can follow the below steps −First of all, create a data frame.Then, use aggregate function to find the sum of rows of a column based on multiple columns.ExampleCreate the data frameLet’s create a data frame as shown below −Grp1
Representing scope information is a concept in which the scope of each variable name is preserved in the symbol table so that we can use the same name in different blocks and different locations.Representing Scope Information involvesA lifetime of a variable in a particular block.Representing name in symbol table along with an indicator of the block in which it appears.Suppose we have a variable name 'a' in block A and the same variable in block B. Suppose we store 'a' in symbol table without block information. In that se, it will only keep the first instance of 'a' which it ... Read More
During compilation, the symbol table is searched each time an identifier is encountered. Data are added if a new name or new information about an existing name is find. Thus, in designing a symbol table structure, it would like a scheme that enables us to insert new entries and identify current entries in a table effectively.There are four symbol tables used in a data structure which are as follows −Lists− The simplest and clear to implement a data structure for a symbol is the linear list of records as displayed in the figure.It can use a single array or several ... Read More
It is a data structure including data for each identifier, fields for the attribute of the identifier. The data structure enables us to find the data for each identifier fastly and to save or retrieve the information for that record quickly.The symbol table is searched each time a name is encountered in the source text. When a new name or new data about an existing name is found, the content of the symbol table modifies. Thus, the symbol table should have an effective structure for creating the data held in the table also for inserting new entries to the symbol ... Read More
The simplest way to execute syntax-directed translation is to use two passes. First, construct a syntax tree for the input and then walk the tree in depth-first order, completing the translations given in definition.The major issue with generating code for Boolean expression and flow of control statements in a single pass is that during a single pass we cannot understand the labels for which the control should goto at the time the jump statements are generated. It can get around this issue by making a sequence of branching statements with the targets of the jumps temporarily left undefined.Each such statement ... Read More
To create bar plot of one column in an R data frame using ggplot2, we can use rownames of the data frame as x variable in aes.For Example, if we have a data frame called df that contains two columns say X and Y and we want to create the bar plot of values in Y then we can use the below mentioned command −ggplot(df,aes(rownames(df),Y))+geom_bar(stat="identity")ExampleFollowing snippet creates a sample data frame −x1
To display infinity and minus infinity symbol in one base R plot, we can use text function and expression function. Inside expression function we can put infinity word for the display of infinity and infinity word with minus sign for the display of minus infinity.Check out the below Examples to understand how it can be done.Example 1To display infinity and minus infinity symbol in one base R plot use the following code −plot(1:10, type="n") text(c(1, 5), expression(-infinity, infinity))OutputIf you execute the above given snippet, it generates the following Output −Example 2To display infinity and minus infinity symbol in one base ... Read More
To display infinity symbol in base R plot, we can use text function and expression function. Inside expression function we can put infinity word for the display of infinity. For Example, if we want to display infinity at position X=2 and Y=4 then we can use the below mentioned command −text(2, 4, expression(infinity))Example 1To display infinity symbol in base R plot, use the snippet given below −plot(1:10, type="n") text(5, 5, expression(infinity))OutputIf you execute the above given snippet, it generates the following Output −Example 2To display infinity symbol in base R plot, use the snippet given below −plot(1:10, type="n") text(5, 5, ... Read More
To subtract all values in a vector from all values in another vector in R, we can use sapply function with subtraction sign.For Example, if we have two vectors say X and Y and we want to subtract all values in Y from all values in X then we can use the command given below −sapply(X,"-",Y)Example 1Following snippet creates a sample data frame −x1