| Command | Description |
|---|---|
getwd() |
This command prints the current working directory in R, which is the directory where R is currently looking for and saving files. |
setwd("path") |
This command sets the current working directory to the directory specified by "path". For example, setwd("/Users/username/Documents") sets the current working directory to the "Documents" folder in the user's home directory. |
x = 10 |
This command assigns the value 10 to the variable x. The type of x is dynamically assigned based on the value it is assigned. In this case, x is assigned as an integer. |
x<-20 |
This command is similar to the previous one, but uses the older assignment operator <- to assign the value 20 to the variable x. |
class(x) |
This command returns the class of the variable x. For example, if x is an integer, class(x) returns "integer". |
x<-as.character(x) |
This command converts the variable x to a character type. If x was previously an integer, it will be converted to a character string representation of the integer. |
x<-as.integer(x) |
This command converts the variable x to an integer type. If x was previously a character, it will be converted to an integer representation of the characters. If the conversion fails, NA is returned. |
v1<-c(1,2,3,4,5) |
This command creates a vector v1 with the elements 1, 2, 3, 4, 5. The c() function is used to concatenate the elements into a single vector. |
v3<-c(v1,v2) |
This command creates a new vector v3 by concatenating the elements of v1 and v2. v1 and v2 must be vectors of the same type for this to work. |
1:10 |
This command creates a vector with the integers from 1 to 10. The : operator is used to create a sequence of integers. |
seq(1,10,by=2) |
This command creates a sequence of numbers from 1 to 10 with a step size of 2. The by parameter specifies the step size. |
seq(1,10,length=4) |
This command creates a sequence of numbers from 1 to 10 with a length of 4. The length parameter specifies the number of elements in the sequence. |
rep(1,5) |
This command creates a vector of length 5 with all elements equal to 1. The first argument specifies the element to be repeated, and the second argument specifies the number of times to repeat it. |
rep(2:4,3) |
This command creates a vector by repeating the elements of 2:4 (i.e., 2, 3, 4) three times. The resulting vector is 2, 3, 4, 2, 3, 4, 2, 3, 4. |
v5[3] |
This command returns the third element of the vector v5. Vector indexing in R starts from 1, so v5[3] returns the value of the third element in v5. |
sort(v6, decreasing = FALSE) |
This command sorts the elements of the vector v6 in ascending order. If decreasing = TRUE, the elements will be sorted in descending order. If decreasing is not specified, it defaults to FALSE. |
| Function | Description |
|---|---|
abs(z) |
This function returns the absolute value of z, which is the distance of z from 0 on the number line. For example, if z is -5, abs(z) will return 5. |
sign(w) |
This function returns the sign of w. If w is positive, it returns 1. If w is negative, it returns -1. If w is zero, it returns 0. |
sqrt(25) |
This function returns the square root of 25, which is 5. |
round(w,1) |
This function rounds w to 1 decimal place. For example, if w is 3.14159, round(w,1) will return 3.1. |
exp(0) |
This function returns the value of e raised to the power of 0, which is 1. |
log(100,10) |
This function returns the logarithm of 100 to the base 10, which is 2. In general, log(x, b) returns the logarithm of x to the base b. |
sin(2*pi) |
This function returns the sine of 2*pi, which is 0. Note that sin takes its argument in radians, so 2*pi corresponds to one complete revolution around the unit circle. The sine of any multiple of pi is 0. |
factorial(5) |
This function returns the factorial of 5, which is 5 * 4 * 3 * 2 * 1, or 120. In general, the factorial of a non-negative integer n is n! = n * (n-1) * (n-2) * ... * 1. |
cumsum(1:5) |
This function returns the cumulative sum of the elements in the vector 1:5. The cumulative sum of a vector is a new vector where each element is the sum of all the previous elements, including itself. For example, cumsum(1:5) returns the vector 1 3 6 10 15, because the cumulative sum of 1:5 is 1 1+2 1+2+3 1+2+3+4 1+2+3+4+5. |
| v7<-c(8,89,65,8,9,1) | This command creates a new vector v7 with the values 8, 89, 65, 8, 9, 1. The c() function is used to concatenate the values into a single vector. The resulting vector v7 has a length of 6. |
| Statistics | Description |
|---|---|
min(v7) |
This command returns the minimum value in the vector v7. In this case, the minimum value in v7 is 1. |
max(v7) |
This command returns the maximum value in the vector v7. In this case, the maximum value in v7 is 89. |
mean(v7) |
This command returns the mean (average) value of the elements in the vector v7. In this case, the mean value of v7 is (8+89+65+8+9+1)/6 = 26.83333. |
var(v7) |
This command returns the variance of the elements in the vector v7. In this case, the variance of v7 is 955.6. |
sd(v7) |
This command returns the standard deviation of the elements in the vector v7. In this case, the standard deviation of v7 is 30.9446. |
cor(v7,v8) |
This command returns the correlation coefficient between the vectors v7 and v8. The correlation coefficient measures the strength and direction of the linear relationship between two variables. If v7 and v8 are of the same length, this command calculates the Pearson correlation coefficient. If v7 and v8 have different lengths, R will recycle the shorter vector to match the length of the longer vector. |
| Functions | Details |
|---|---|
v7 == 89 |
This command returns a logical vector of the same length as v7, where each element is TRUE if the corresponding element in v7 is equal to 89, and FALSE otherwise. In this case, the resulting logical vector is FALSE, TRUE, FALSE, FALSE, FALSE, FALSE. |
which(v7==8) |
This command returns a vector of indices where the elements in v7 are equal to 8. The which() function returns the indices of a logical vector that are TRUE. In this case, the resulting vector is 1 4, because the first and fourth elements of v7 are equal to 8. |
| which(v7<=8) | This command returns a vector of indices where the elements in v7 are less than or equal to 8. The resulting vector contains the indices of all the elements in v7 that are less than or equal to 8. In this case, the resulting vector is 1 4 6, because the first, fourth, and sixth elements of v7 are less than or equal to 8. |
any(v7==2) |
This command returns a logical value FALSE because there is no element in the vector v7 that is equal to 2. The any() function returns TRUE if at least one element of a logical vector is TRUE, and FALSE otherwise. Since there is no element in v7 equal to 2, the expression v7==2 evaluates to a logical vector of FALSEs, and so any(v7==2) returns FALSE. |
all(v7>0) |
This command returns a logical value TRUE because all the elements of v7 are greater than 0. The all() function returns TRUE if all the elements of a logical vector are TRUE, and FALSE otherwise. Since all the elements of v7 are greater than 0, the expression v7>0 evaluates to a logical vector of all TRUEs, and so all(v7>0) returns TRUE. |
! v7 == 225 |
This command returns a logical vector of the same length as v7, where each element is TRUE if the corresponding element in v7 is not equal to 225, and FALSE otherwise. The ! operator is used to negate the logical vector obtained from v7 == 225. In this case, the resulting logical vector is TRUE, TRUE, TRUE, TRUE, TRUE, TRUE. |
any(v7>50) & any(v7<100) |
This command returns a logical value TRUE because at least one element of v7 is greater than 50 and at least one element of v7 is less than 100. The any() function is used to check if there is at least one element of v7 that satisfies a condition, and the & operator is used to check if both conditions are TRUE. In this case, the first condition any(v7>50) is TRUE because there is at least one element in v7 that is greater than 50 (89). The second condition any(v7<100) is also TRUE because all the elements in v7 are less than 100. Since both conditions are TRUE, the entire expression returns TRUE. |
| Matrix | Details |
|---|---|
m<-matrix(1:6,nrow=3,ncol=2) |
This command creates a new matrix m with 3 rows and 2 columns, and fills it with the values 1, 2, 3, 4, 5, 6. The matrix() function is used to create a matrix with the specified number of rows and columns, and the nrow and ncol parameters are used to specify the number of rows and columns, respectively. The values to be filled in the matrix are provided as the first argument to matrix(), in this case, the values 1:6. |
m<-matrix(1:6,nrow=3,byrow= TRUE) |
This command creates a new matrix m with 3 rows and 2 columns, and fills it with the values 1, 2, 3, 4, 5, 6. The matrix() function is used to create a matrix with the specified number of rows and columns, and the nrow parameter is used to specify the number of rows. The byrow parameter is set to TRUE to indicate that the values should be filled in row-wise, rather than column-wise. |
dim(m) |
This command returns the dimensions of the matrix m, which is a vector with two elements representing the number of rows and columns in the matrix, respectively. In this case, since m has 3 rows and 2 columns, the resulting vector is 3 2. The command dim(m) is equivalent to c(nrow(m), ncol(m)). |
m[2,2] |
This command retrieves the value of the element in the second row and second column of the matrix m. In this case, the value is 4. |
m[1,] |
This command retrieves all the values in the first row of the matrix m. The comma , is used to indicate that we want to retrieve all the columns in the first row. In this case, the resulting vector is 1 2. |
m[,2] |
This command retrieves all the values in the second column of the matrix m. The comma , is used to indicate that we want to retrieve all the rows in the second column. In this case, the resulting vector is 2 4 6. |
m[c(2,3),] |
This command retrieves all the values in the second and third rows of the matrix m. The c(2,3) argument is used to specify the row indices we want to retrieve. The comma , is used to indicate that we want to retrieve all the columns in the specified rows. |
m[m>3] |
This command retrieves all the values in the matrix m that are greater than 3. The logical expression m > 3 is evaluated for each element in the matrix, and returns a matrix of the same dimensions as m with TRUE values where the corresponding element in m is greater than 3, and FALSE values otherwise.The resulting matrix contains all the values in m that are greater than 3, arranged in a vector. In this case, the resulting vector is 4 5 6, because those are the values in m that are greater than 3. The resulting vector is arranged in column-major order, which means that the values are listed column by column, starting from the first column. |
m>3 |
This command returns a logical matrix of the same dimensions as m, where each element is TRUE if the corresponding element in m is greater than 3, and FALSE otherwise. The logical expression m > 3 is evaluated for each element in the matrix, and returns a matrix of the same dimensions as m with TRUE values where the corresponding element in m is greater than 3, and FALSE values otherwise. |
m[m%%2==0] |
This command retrieves all the values in the matrix m that are even. The expression m %% 2 == 0 is evaluated for each element in the matrix, and returns a matrix of the same dimensions as m with TRUE values where the corresponding element in m is even (i.e. divisible by 2), and FALSE values otherwise. The resulting matrix contains all the values in m that are even, arranged in a vector. In this case, the resulting vector is 2 4 6, because those are the values in m that are even. The resulting vector is arranged in column-major order, which means that the values are listed column by column, starting from the first column. |
t(m) |
This command transposes the matrix m, which means it switches its rows and columns. The t() function is used to transpose a matrix. In this case, the resulting matrix has 2 rows and 3 columns. The first row contains the values 1, 3, 5, and the second row contains the values 2, 4, 6. You are correct that if we accidentally set the number of columns as nrow and the number of rows as ncol while creating a matrix, we can use the t() function to transpose the matrix and get the correct orientation. |
m * tm |
- m * tm is element-wise multiplication, also known as the Hadamard product. It multiplies each element in m by the corresponding element in tm, and the resulting matrix has the same dimensions as m and tm. The resulting matrix is not necessarily a valid matrix product, and its interpretation and use depends on the context of the problem being solved. |
m %*% tm |
- m %*% tm is matrix multiplication, which performs the dot product between each row in m and each column in tm. It results in a new matrix with the same number of rows as m and the same number of columns as tm. Matrix multiplication is a fundamental operation in linear algebra and is used for a variety of applications, such as solving systems of linear equations and computing eigenvectors and eigenvalues. |
tip for m %*% tm and m * tm |
It's important to note that these are different operations and should not be used interchangeably. The resulting matrices are generally different, and their interpretation and use depend on the context of the problem being solved. |
| Command - Con-cat | Details |
|---|---|
m3<-cbind(tm,c(11,12)) |
This command creates a new matrix m3 by column-binding the matrix tm with a new vector containing the values 11 and 12. The cbind() function is used to column-bind matrices and vectors together. In this case, since tm is a 2x3 matrix and the new vector is a 1x2 vector, the resulting matrix m3 is a 2x5 matrix. The cbind() function aligns the dimensions of the matrices and vectors by filling in missing values with NA. The first three columns contain the values from tm, and the last two columns contain the values 11 and 12. Since the new vector only has two values, the third row of m3 contains NA values to fill in the missing values. |
m4<-rbind(m3,c(8,8,8) |
This command creates a new matrix m4 by row-binding the matrix m3 with a new vector containing the values 8, 8, 8. The rbind() function is used to row-bind matrices and vectors together. In this case, since m3 is a 2x5 matrix and the new vector is a 1x3 vector, the resulting matrix m4 is a 3x5 matrix. The rbind() function aligns the dimensions of the matrices and vectors by filling in missing values with NA. |
colnames(m4)<-c('col1','col2') rownames(m4)<-c('col1','col2','col2','col2','col2') |
These commands assign new row and column names to the matrix m4. The command colnames(m4) <- c('col1', 'col2') assigns the column names col1 and col2 to the two columns of m4. The colnames() function is used to get or set the column names of a matrix or data frame. In this case, the c() function is used to create a character vector containing the new column names. The command rownames(m4) <- c('col1', 'col2', 'col2', 'col2', 'col2') assigns the row names col1, col2, col2, col2, and col2 to the five rows of m4. The rownames() function is used to get or set the row names of a matrix or data frame. In this case, the c() function is used to create a character vector containing the new row names. |
Written with StackEdit.