[R] 제어문

작성일자 : 2023-09-29

Ver 0.1.1

if() function

• if( cond ) expr
• if( cond ) cond.expr else alt.expr

x = 1:5
x

## [1] 1 2 3 4 5

y = -2:2
y

## [1] -2 -1  0  1  2

if ( any( x < 0 ) ) print( x )     # print() is not executed
if ( any( y < 0 ) ) print( abs( y ) )     # print() is executed

## [1] 2 1 0 1 2

if ( any( y < 0 ) ) {
  print( abs( y ) )
  print( 'y contains negative values' )
}

## [1] 2 1 0 1 2

## [1] "y contains negative values"

if ( pi > 3 ) print( 'expr if statement' ) else print( 'expre else statement' )

## [1] "expr if statement"

if( pi < 3 ) print( 'expr if statement' ) else print( 'expr else statement' )

## [1] "expr else statement"

# multiple conditions
if ( length( x ) == 5 ) {
  if ( sum( x ) == 15 ) print( 'Vector x length=5, sum=15' )
} else {
  print( 'Vector x length!=5' )
}

## [1] "Vector x length=5, sum=15"

# alternative form of multiple conditions
if( length( x ) == 5 && sum( x ) == 15 ) {
  print( 'Vector x length=5, sum=15' )
} else {
  print( 'Vector x length!=5' )
}

## [1] "Vector x length=5, sum=15"

 

ifelse() function

• ifelse( test, yes, no )

y = -2:2
ifelse ( y >= 0 , y , -y )

## [1] 2 1 0 1 2

abs( y )

## [1] 2 1 0 1 2

tmp = 3
ifelse ( tmp > 0 , 'positive' , ifelse( tmp < 0 , 'negative' , 'zero' ) )

## [1] "positive"

 

switch() function

• switch( EXPR , value1 , value2 , ... )

x = 1:10
switch( EXPR = 1 , mean( x ) , median( x ) , sd( x ) , range( x ) )

## [1] 5.5

switch( EXPR = 2 , mean( x ) , median( x ) , sd( x ) , range( x ) )

## [1] 5.5

switch( EXPR = 3 , mean( x ) , median( x ) , sd( x ) , range( x ) )

## [1] 3.02765

switch( EXPR = 4 , mean( x ) , median( x ) , sd( x ) , range( x ) )

## [1]  1 10

switch( EXPR = 5 , mean( x ) , median( x ) , sd( x ) , range( x ) )

x = 1:10
type = 'mean'
switch( EXPR = type ,
        MEAN = , mean = mean( x ) ,
        MEDIAN = , median = median( x ) ,
        SD = , sd = sd( x ) ,
        range( x ) )

## [1] 5.5

type = 'SD'
switch( EXPR = type ,
        MEAN = , mean = mean( x ) ,
        MEDIAN = , median = median( x ) ,
        SD = , sd = sd( x ) ,
        range( x ) )

## [1] 3.02765

type = 'Sd'
switch( EXPR = type ,
        MEAN = , mean = mean( x ) ,
        MEDIAN = , median = median( x ) ,
        SD = , sd = sd( x ) ,
        range( x ) )

## [1]  1 10

 

Loop statements

• for( var in seq ) expr
• while( cond ) expr
• repeat expr

for ( i in 5:1 ) print( rep( i , i ) )

## [1] 5 5 5 5 5

## [1] 4 4 4 4

## [1] 3 3 3

## [1] 2 2

## [1] 1

sum.x = 0

# sum from 1 to 10
for ( i in 1:10 ) 
  sum.x = sum.x + i
sum.x

## [1] 55

# form a multiplication table
for ( i in 2:9 )
  for( j in 1:9 )
    cat( i , '*' , j , '=' , i * j , '\n' )

## 2 * 1 = 2 

## 2 * 2 = 4 

## 2 * 3 = 6 

## 2 * 4 = 8 

## 2 * 5 = 10 

## 2 * 6 = 12 

## 2 * 7 = 14 

## 2 * 8 = 16 

## 2 * 9 = 18 

## 3 * 1 = 3 

## 3 * 2 = 6 

## 3 * 3 = 9 

## 3 * 4 = 12 

## 3 * 5 = 15 

## 3 * 6 = 18 

## 3 * 7 = 21 

## 3 * 8 = 24 

## 3 * 9 = 27 

## 4 * 1 = 4 

## 4 * 2 = 8 

## 4 * 3 = 12 

## 4 * 4 = 16 

## 4 * 5 = 20 

## 4 * 6 = 24 

## 4 * 7 = 28 

## 4 * 8 = 32 

## 4 * 9 = 36 

## 5 * 1 = 5 

## 5 * 2 = 10 

## 5 * 3 = 15 

## 5 * 4 = 20 

## 5 * 5 = 25 

## 5 * 6 = 30 

## 5 * 7 = 35 

## 5 * 8 = 40 

## 5 * 9 = 45 

## 6 * 1 = 6 

## 6 * 2 = 12 

## 6 * 3 = 18 

## 6 * 4 = 24 

## 6 * 5 = 30 

## 6 * 6 = 36 

## 6 * 7 = 42 

## 6 * 8 = 48 

## 6 * 9 = 54 

## 7 * 1 = 7 

## 7 * 2 = 14 

## 7 * 3 = 21 

## 7 * 4 = 28 

## 7 * 5 = 35 

## 7 * 6 = 42 

## 7 * 7 = 49 

## 7 * 8 = 56 

## 7 * 9 = 63 

## 8 * 1 = 8 

## 8 * 2 = 16 

## 8 * 3 = 24 

## 8 * 4 = 32 

## 8 * 5 = 40 

## 8 * 6 = 48 

## 8 * 7 = 56 

## 8 * 8 = 64 

## 8 * 9 = 72 

## 9 * 1 = 9 

## 9 * 2 = 18 

## 9 * 3 = 27 

## 9 * 4 = 36 

## 9 * 5 = 45 

## 9 * 6 = 54 

## 9 * 7 = 63 

## 9 * 8 = 72 

## 9 * 9 = 81

 

break 과 next

• break
• next

sum.x = 0
for ( i in 1:10 ) {
  sum.x = sum.x + i
  if ( sum.x > 20 ) break
  cat( i , sum.x , '\n' )
}

## 1 1 

## 2 3 

## 3 6 

## 4 10 

## 5 15

 

for ( i in 2:9 ) {
  if ( i > 5 ) break
  for ( j in 1:9 ) {
    if ( j > 1 ) break
    cat( i , '*' , j , '=' , i * j , '\n' )
  }
}

## 2 * 1 = 2 

## 3 * 1 = 3 

## 4 * 1 = 4 

## 5 * 1 = 5

 

x = 0
sum.x = 0
while ( x < 10 ) {
  x = x + 1
  if ( x < 9 ) next
  print( x )
  sum.x = sum.x + x
}

## [1] 9

## [1] 10

sum.x

## [1] 19