15.1 Exercise 10: If statement

Create the script “exercise10.R” and save it to the “Rcourse/Module2” directory: you will save all the commands of exercise 10 in that script.
Remember you can comment the code using #.

correction

getwd()
setwd("~/Rcourse/Module2")

1- Create vector vec2 as:

vec2 <- c("kiwi", "apple", "pear", "grape")

• Use an if statement and the %in% function to check whether “apple” is present in vec2 (in such case print “there is an apple!”)

correction

if("apple" %in% vec2){
    print("there is an apple there")
}

## [1] "there is an apple there"

• Use an if statement and the %in% function to check whether “grapefruit” is present in vec2: if “grapefruit” is not found, test for a second condition (using else if) that checks if “pear” is found.

correction

if("grapefruit" %in% vec2){
        print("there is a grapefruit there")
}else if("pear" %in% vec2){
    print("there is no grapefruit but there is a pear")
}

## [1] "there is no grapefruit but there is a pear"

• Add an else section in case neither grapefruit nor pear is found in vec2.
  Test your if statement also on vec3:

vec3 <- c("cherry", "strawberry", "blueberry", "peach")

correction

if("grapefruit" %in% vec2){
        print("there is a grapefruit there")
}else if("pear" %in% vec2){
        print("there is no grapefruit but there is a pear")
}else{
    print("no grapefruit and no pear")
}

## [1] "there is no grapefruit but there is a pear"

2- If statement in for loop

Create the following matrix:

mat4 <- matrix(c(2, 34, 1, NA, 89, 7, 12, NA, 0, 38),
    nrow=5)

Loop over rows with for of mat4 and print row number and entire row if you find an NA.

correction

for(k in 1:nrow(mat4)){
    # extract row
    rowk <- mat4[k,]
    if(any(is.na(rowk))){
        print(k)
        print(rowk)
    }
}

## [1] 3
## [1]  1 NA
## [1] 4
## [1] NA  0

3- For loop, if statement and regular expression

Create vector vec4 as:

vec4 <- c("Oct4", "DEPP", "RSU1", "Hk2", "ZNF37A", "C1QL1", "Shh", "Cdkn2a")

Loop over each element of “vec4”: * If the element is a human gene (all upper-case characters), print a vector of two elements: the name of the gene and “human gene”.
* If the element is a mouse gene (only the first character is in upper-case), print a vector of two elements: the name of the gene and “mouse gene”.

Tip 1: Use grep and a regular expression in the if statement !
Tip 2: When grep does not find a match, it returns an element of length 0 !
Tip 3: You can also use grepl: check the help page

correction

for(gene in vec4){
    if(length(grep(pattern="^[A-Z0-9]+$", x=gene)) != 0){
        print(c(gene, "human gene"))
    }else if(length(grep(pattern="^[A-Z]{1}[a-z0-9]+$", x=gene)) != 0){
        print(c(gene, "mouse gene"))
    }
}

## [1] "Oct4"       "mouse gene"
## [1] "DEPP"       "human gene"
## [1] "RSU1"       "human gene"
## [1] "Hk2"        "mouse gene"
## [1] "ZNF37A"     "human gene"
## [1] "C1QL1"      "human gene"
## [1] "Shh"        "mouse gene"
## [1] "Cdkn2a"     "mouse gene"

# With grepl
for(gene in vec4){
        if(grepl(pattern="^[A-Z0-9]+$", x=gene)){
                print(c(gene, "human gene"))
        }else if(grepl(pattern="^[A-Z]{1}[a-z0-9]+$", x=gene)){
                print(c(gene, "mouse gene"))
        }
}

## [1] "Oct4"       "mouse gene"
## [1] "DEPP"       "human gene"
## [1] "RSU1"       "human gene"
## [1] "Hk2"        "mouse gene"
## [1] "ZNF37A"     "human gene"
## [1] "C1QL1"      "human gene"
## [1] "Shh"        "mouse gene"
## [1] "Cdkn2a"     "mouse gene"