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Page 1226 of 2109
Lonely Pixel I in C++
Suppose we have a picture consisting of black and white pixels, we have to find the number of black lonely pixels. Here the picture is represented by a 2D char array consisting of 'B' and 'W', for the black and white pixels respectively.A black lonely pixel is actually 'B' that located at a specific position where the same row and same column don't have any other black pixels.If the input is like −WWBWBWBWWOutput will be 3. Because all the three 'B's are black lonely pixels.To solve this, we will follow these steps −n := size of picturem := (if n ...
Read MoreHow to extract columns based on particular column values of an R data frame that matchna pattern?
The column values of an R data frame can be easily extracted by subsetting with single square brackets but if we want to extract the column values that match a pattern then we need to use grepl function inside single square brackets, this will help us to match the pattern of the values in the data frame columns.ExampleConsider the below data frame:> set.seed(271) > x1 x2 df1 df1Output x1 x2 1 A242 B71 2 A123 B71 3 A242 B81 4 A242 B87 5 A123 B71 6 A321 B71 7 A187 ...
Read MoreHow to perform post hoc test for Kruskal-Wallis in R?
The Kruskal-Wallis test is the non-parametric analogue of one-way analysis of variance. The non-parametric tests are used in situations when the assumptions of parametric tests are not met. If we find significant difference in Kruskal-Wallis then post hoc tests are done to find where the difference exists. For this purpose, we can perform dunn test. The function of dunn test can be accessed through FSA package.Example1Loading FSA package:> library(FSA)Consider the below data frame:> x1 y1 df1 df1Output x1 y1 1 E 1.1191117 2 D 1.1276032 3 D 1.5610692 4 E 1.1585054 5 E 1.0239322 6 C 0.8000165 ...
Read MoreHow to check if some specific columns of an R data frame are equal to a column or not?
If we have a large amount of data in a data frame and we suspect that some of the data columns are repeated or some of them are equal to a particular column then we can use sapply function in base R to figure it out. In this way, we can remove duplicated columns that does not suppose to help in our data analysis objective.Example1Consider the below data frame:> set.seed(354) > x1 x2 x3 x4 x5 df1 df1Outputx1 x2 x3 x4 x5 1 4 5 4 4 6 2 6 4 8 7 5 3 5 6 4 7 6 ...
Read MoreHow to create a vector of lists in R?
If we have many lists but we want to use the values in the lists as a vector then we first need to combine those lists and create a vector. This can be done by using unlist function along with the combine function c to create the vector. For example, if we have two lists defined as List1 and List2 and we want to create a vector V using these lists then it can be created as:V x1 x1Output$a [1] -0.6972237 -1.5013768 -0.2451809 -0.2365569 -1.6304919 -1.1704378 [7] 1.1617054 -0.2349498 -1.2582229 0.4112065 $b [1] 2 0 2 6 0 0 ...
Read MoreHow to perform chi square test for goodness of fit in R?
The chi square test for goodness of fit is a nonparametric test to test whether the observed values that falls into two or more categories follows a particular distribution of not. We can say that it compares the observed proportions with the expected chances. In R, we can perform this test by using chisq.test function. Check out the below examples to understand how it is done.Example1> x1 x1Output[1] 9 4 1 9 6 6 1 6 0 0 5 8 8 3 7 8 0 3 3 9 6 0 3 8 2 0 8 5 9 1 3 4 ...
Read MoreHow to subset nth row from an R data frame?
We can find subsets using many ways in R and the easiest way is to use single-square brackets. If we want to subset a row or a number of consecutive or non-consecutive rows then it can be directly done with the data frame name and the single-square brackets. For example, if we have a data frame called df and we want to subset 1st row of df then we can use df[1, ] and that’s it.ExampleConsider the below data frame:> set.seed(214) > x y z a b c q w df1 df1Outputx y z a b c q w 1 ...
Read MoreHow to extract the names of list elements in R?
The names of list elements can be extracted by using the names function. For example, if we have a list defined as List that contains three elements with names element1, element2, and element3 then then these names can be extracted from the List by using the below command:names(List)Example1> List1 List1Output$x1 [1] -0.04518909 -0.22779868 0.24339595 -0.86189295 -0.73387277 -0.75313131 [7] 0.39694608 2.30565359 0.55670193 0.21973762 0.62968128 -0.90936921 [13] 1.33946741 -0.16315751 0.31357793 0.40365980 -0.23639612 -2.48749453 [19] 0.52152768 -1.57059863 0.51728464 0.98177111 0.65475629 0.23715538 [25] -0.71796609 -0.42731839 0.32335282 -0.90013122 -0.84549927 -0.88358214 [31] -0.32066379 -0.98945433 0.42469849 -1.63095343 0.32584448 0.10947333 [37] 0.23486625 0.28166351 1.18432843 0.94828212 0.09452671 0.56618262 [43] ...
Read MoreHow to create a function in R with two inputs?
To create a function with two inputs, we just need to provide two different arguments inside function. For example, if we want to create a function to find the square of a+b then we can use x and y inside function. Check out the below examples to understand how we can do it.Example1> F F(x=1, y=1) > F(x=2, y=3) > F(x=c(1, 2), y=c(2, 3))Output[1] 4 [1] 25 [1] 9 25Example> F(x=rpois(50, 2), y=rpois(50, 7))Output[1] 36 169 121 36 49 100 144 169 144 81 100 256 121 121 36 64 49 225 121 [20] 16 64 100 36 64 ...
Read MoreHow to extract columns of a data frame with their names after converting it to a time series object in R?
To access columns of data frame in R, we just need to use $ sign but if the data frame is converted to a time series object then all the columns will behave as a time series, hence, we cannot simply use $ sign. For this purpose, we would need to use single square brackets and pass the appropriate column inside it. Look at the below examples to understand how it works.Example 1Consider the below data frame:> set.seed(147) > x1 x2 x3 df1 df1Outputx1 x2 x3 1 5 11 4 2 5 5 3 3 4 6 2 4 10 ...
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