Programming Articles - Page 1364 of 3366

In data science, we often face the problem of missing values and we need to define a way to replace them with an appropriate value or we can complete remove them. If we want to replace the missing then we also need to know how many missing values are there. Therefore, if we have a data frame with grouping column then finding the number of groupwise missing values can be done with aggregate function as shown in the below examples.Example1Consider the below data frame −Live Demo> Group x df1 df1Output   Group  x 1      A  2 2     ... Read More

The standardization of a numerical column can be easily done with the help of scale function but if we want to standardize multiple columns of a data frame if categorical columns also exist then mutate_if function of dplyr package will be used. For example, if we have a data frame df then it can be done as df%>%mutate_if(is.numeric, scale)Example1Consider the below data frame −Live Demo> x1 x2 df1 df1Output   x1 x2 1   c  4 2   c  1 3   a  4 4   a  1 5   b  0 6   c  4 7   c  2 8 ... Read More

To create a bar plot in base R with different limits for Y-axis, we can use ylim argument but generally that behaves badly, such as extending the bars below X-axis. Therefore, we need to fix those things. Check out the below example to understand how it can be done.Example> x barplot(x)OutputExample> barplot(x,ylim=c(300,600))OutputExample> barplot(x,ylim=c(300,600),xpd=FALSE)OutputExample> box(bty="l") Output

The value of the pointer address is constant that means we cannot change the value of the address that is pointed by the pointer.A constant pointer is declared as follows −Data_Type const* Pointer_Name;For example, int const *p// pointer to const integerExampleFollowing is the C program to illustrate a pointer to a constant −#include int main(void){    int var1 = 100;    // pointer to constant integer    const int* ptr = &var1;    //try to modify the value of pointed address    *ptr = 10;    printf("%d", *ptr);    return 0; }OutputWhen the above program is executed, it produces the ... Read More

Double pointer or pointer to pointer is a variable that holds the address of another pointer.Following is the declaration for a pointer to a pointer −datatype ** pointer_name;For example, int **p; p is a pointer to pointerInitialization − ‘&’ is used for initialization.For example, int a = 10; int *p; int **q; p = &a;Accessing − Indirection operator (*) is used for accessing.ExampleFollowing is the C program for the pointer to pointer − Live Demo#include main ( ){    int A = 10;    int *p;    int **q;    p = &A;    q = &p;    printf("A =%d", A); ... Read More

If we have a colour column in an R data frame and we want to change the point colours in ggplot2 using that column then colour argument will be used. For example, if we have a data frame called df that contains three columns say x, y, and color then the scatterplot between x and y with the colour of points using color column can be created by using the command ggplot(df, aes(x, y))+geom_point(colour=df$color)ExampleConsider the below data frame −Live Demo> x y col df dfOutput             x          y   col 1   ... Read More

To match a column in a data frame with a column in another data frame, we can use match function. For example, if we have two data frames called df1 and df2 each having one similar column and the second having an extra column then the matching can be done for similar columns and a new column in the first data frame can be created based on that match and the second column the second data frame. Check out the below examples to understand how it works.Example1Live Demo> df1 df1Output   x1 1   2 2   2 3   1 ... Read More

The length of columns for missing values means the number of missing values in the data frame. This can be easily done with the help of colSums function where we will find the total number of NA values with is.na. For example, if we have a data frame called df that contains some missing values then the length of columns for missing values can be found by using the command colSums(is.na(df)).Example1Consider the below data frame −Live Demo> x1 x2 x3 x4 df1 df1Output   x1 x2 x3 x4 1  NA NA  2  2 2  NA NA NA  2 3   1 ... Read More

To add suffix to column names in R, we can use paste function. For example, if we have a data frame called df that contains three columns say x, y, and z and we want to add a suffix to these columns say underscore1 (_1) then it can be done by using the commandcolnames(df) x y z df1 df1Output   x y z 1  6 3 2 2  9 7 5 3  5 7 6 4  5 9 6 5  2 5 9 6  4 5 4 7  2 0 7 8  2 5 8 9  4 5 8 10 6 ... Read More

To add a vector to reach row of a matrix, we can use addition sign (+) and create the repetition of the vector up to the number of rows in the matrix. For example, if we have a matrix called M then a vector say v can be added to each row of M by using the command −M+rep(v, each=nrow(M))Example1Consider the below matrix and the vector −Live Demo> M1 M1Output      [, 1] [, 2]  [1, ]    3    2  [2, ]    3    3  [3, ]    4    2  [4, ]    5    1 ... Read More