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Articles on Trending Technologies
Technical articles with clear explanations and examples
What is Representing Scope Information?
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 MoreWhat is role of different data structures in compiler design?
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 MoreWhat is Backpatching of Boolean Expressions and Control Statements in compiler design?
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 MoreHow to display infinity symbol in base R plot?
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 MoreR programming to subtract all values in a vector from all values in another vector.
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
Read MoreR programming to find the sum of corresponding elements in all matrix's stored in a list.
To find the sum of corresponding elements in all matrix’s stored in a list in R, we can use Reduce function with plus sign. For Example, if we have a list called LIST that contains multiple matrices and we want to find the sum of corresponding elements then we can use the command given below −Reduce("+",LIST)Check out the below Examples to understand how it works.Example 1To find the sum of corresponding elements in all matrix’s stored in a list in R, use the following snippet −List
Read MoreHow to find the sum of all array elements in R?
To find the sum of all array elements in R, we can use Reduce function with plus sign. For Example, if we have an array called ARRAY and we want to find the sum of all values in this array then we can use the command Reduce("+",ARRAY).Check out the below Examples to understand how it works.Example 1To find the sum of all array elements in R use the snippet given below −Array1
Read MoreExtract a data frame column values as a vector by matching a vector in R.
To extract a data frame column values as a vector by matching a vector in R, we can use subsetting with %in% operator.For Example, if we have a data frame called df having a column say C and a vector V and we want to extract values in C if they match with V then we can use the command given below −df[df$C %in% V,"C"]Example 1Following snippet creates a sample data frame and vector −x1
Read MoreWhat is representation of fixed-length and variablelength array representation in the symbol table?
Symbol Table is a data structure that supports an effective and efficient way of storing data about various names occurring in the source code. These names are used in the source code to identify the different program elements, like a variable, constants, procedures, and the labels of statements.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 ...
Read MoreHow to change the name of single column using setNames in R?
To change the name of single column using setNames, we would need to specify the column name that needs to be changed.For example, if we have a data frame called df that contains three columns say Var1, var2, and Var3 and we want to change var2 to Var2 then we can use the command as follows −setNames(df,replace(names(df),names(df)=="var2","Var2"))Example 1Following snippet creates a sample data frame −x
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