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If we have a data frame that contains a column of column names which matches with the column names of a data frame and another column that has different values then we can set these different values as the new column names of the data frame having matched column names.This can be done with the help of match function. Check out the below Examples to understand how it works.Example 1Following snippet creates a sample data frame −x1
To convert a data frame with grouping column into a list based on groups, we can use split function.For Example, if we have a data frame called df that contains a categorical column say Group and a numerical column say DV then we can convert df into a list based on groups in Group column by using the command as mentioned below −split(df$DV,df1$Group).Example 1Following snippet creates a sample data frame −Group
If we have a square matrix or we want to create a square matrix and the row names and column names for this matrix are same then we can define these names in a single line of code.For Example, if we have a matrix called M that has 10 rows and 10 columns that has first ten alphabets as row and column names then we can define the column names as colnames(M)
Generally, the duplicate values are considered after first occurrence but the first occurrence of a value is also a duplicate of the remaining. Therefore, we might want to exclude that as well.The subsetting of non-duplicate values from an R data frame column can be easily done with the help of duplicated function with negation operator as shown in the below Examples.Example 1Following snippet creates a sample data frame −x
Recursive Descent Parser uses the technique of Top-Down Parsing without backtracking. It can be defined as a Parser that uses the various recursive procedure to process the input string with no backtracking. It can be simply performed using a Recursive language. The first symbol of the string of R.H.S of production will uniquely determine the correct alternative to choose.The major approach of recursive-descent parsing is to relate each non-terminal with a procedure. The objective of each procedure is to read a sequence of input characters that can be produced by the corresponding non-terminal, and return a pointer to the root ... Read More
There are two types of Top-Down Parsing without Backtracking, which are as follows −Recursive Descent ParserPredictive ParserRecursive Descent ParserA top-down parser that implements a set of recursive procedures to process the input without backtracking is known as recursive-descent parser, and parsing is known as recursive-descent parsing. The recursive procedures can be accessible to write and adequately effective if written in a language that performs the procedure call effectively.There is a procedure for each non-terminal in the grammar. It can consider a global variable lookahead, influencing the current input token and a procedure match (Expected Token) is the action of recognizing ... Read More
A Grammar G (V, T, P, S) is left recursive if it has a production in the form.A → A α |β.The above Grammar is left recursive because the left of production is occurring at a first position on the right side of production. It can eliminate left recursion by replacing a pair of production withA → βA′A → αA′|ϵThe general form for left recursion isA → Aα1|Aα2| … . |Aαm|β1|β2| … . . βncan be replaced byA → β1A′|β2A′| … . . | … . . |βnA′A → α1A′|α2A′| … . . |αmA′|εIn the following grammar, it does not ... Read More
In Top-Down Parsing with Backtracking, Parser will attempt multiple rules or production to identify the match for input string by backtracking at every step of derivation. So, if the applied production does not give the input string as needed, or it does not match with the needed string, then it can undo that shift.Example1 − Consider the GrammarS → a A dA → b c | bMake parse tree for the string a bd. Also, show parse Tree when Backtracking is required when the wrong alternative is chosen.SolutionThe derivation for the string abd will be −S ⇒ a A d ⇒ ... Read More
Precedence relations between any two operators or symbols in the precedence table can be converted to two precedence functions f & g that map terminals symbols to integers.If a g (b)Here a, b represents terminal symbols. f (a) and g (b) represents the precedence functions that have an integer value.Computations of Precedence FunctionsFor each terminal a, create the symbol fa&ga.Make a node for each symbol. If a =. b, then fa & gb are in same group or node. If a =. b & c =. b, ... Read More
OPG stands for Operator Precedence Grammar. Grammar with the later property is known as operator precedence grammar. It is ε −free Operator Grammar in which precedence relation are disjoint, i.e., If a . > b exists, then b .> a will not exist.Example1 − Verify whether the following Grammar is operator Grammar or not.E → E A E |(E)|idA → +| − | *SolutionNo, it is not an operator Grammar as it does not satisfy property 2 of operator Grammar.As it contains two adjacent Non-terminals on R.H.S of production E → E A E .We can convert it into ... Read More