220409

data(iris)
head(iris);tail(iris)

##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1          5.1         3.5          1.4         0.2  setosa
## 2          4.9         3.0          1.4         0.2  setosa
## 3          4.7         3.2          1.3         0.2  setosa
## 4          4.6         3.1          1.5         0.2  setosa
## 5          5.0         3.6          1.4         0.2  setosa
## 6          5.4         3.9          1.7         0.4  setosa

##     Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
## 145          6.7         3.3          5.7         2.5 virginica
## 146          6.7         3.0          5.2         2.3 virginica
## 147          6.3         2.5          5.0         1.9 virginica
## 148          6.5         3.0          5.2         2.0 virginica
## 149          6.2         3.4          5.4         2.3 virginica
## 150          5.9         3.0          5.1         1.8 virginica

names(iris)

## [1] "Sepal.Length" "Sepal.Width"  "Petal.Length" "Petal.Width"  "Species"

names(iris)<-tolower(names(iris))
names(iris)

## [1] "sepal.length" "sepal.width"  "petal.length" "petal.width"  "species"

iris<-iris[1:4]
head(iris)

##   sepal.length sepal.width petal.length petal.width
## 1          5.1         3.5          1.4         0.2
## 2          4.9         3.0          1.4         0.2
## 3          4.7         3.2          1.3         0.2
## 4          4.6         3.1          1.5         0.2
## 5          5.0         3.6          1.4         0.2
## 6          5.4         3.9          1.7         0.4

names(iris)<-c('sl','sw','pl','pw')
head(iris)

##    sl  sw  pl  pw
## 1 5.1 3.5 1.4 0.2
## 2 4.9 3.0 1.4 0.2
## 3 4.7 3.2 1.3 0.2
## 4 4.6 3.1 1.5 0.2
## 5 5.0 3.6 1.4 0.2
## 6 5.4 3.9 1.7 0.4

m2<-lm(sl~.,data=iris)
summary(m2)

## 
## Call:
## lm(formula = sl ~ ., data = iris)
## 
## Residuals:
##      Min       1Q   Median       3Q      Max 
## -0.82816 -0.21989  0.01875  0.19709  0.84570 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)    
## (Intercept)  1.85600    0.25078   7.401 9.85e-12 ***
## sw           0.65084    0.06665   9.765  < 2e-16 ***
## pl           0.70913    0.05672  12.502  < 2e-16 ***
## pw          -0.55648    0.12755  -4.363 2.41e-05 ***
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 0.3145 on 146 degrees of freedom
## Multiple R-squared:  0.8586, Adjusted R-squared:  0.8557 
## F-statistic: 295.5 on 3 and 146 DF,  p-value: < 2.2e-16

step(m2,direction = "both")

## Start:  AIC=-343.04
## sl ~ sw + pl + pw
## 
##        Df Sum of Sq    RSS     AIC
## <none>              14.445 -343.04
## - pw    1    1.8834 16.329 -326.66
## - sw    1    9.4353 23.881 -269.63
## - pl    1   15.4657 29.911 -235.86

## 
## Call:
## lm(formula = sl ~ sw + pl + pw, data = iris)
## 
## Coefficients:
## (Intercept)           sw           pl           pw  
##      1.8560       0.6508       0.7091      -0.5565

step(m2,direction = "forward")

## Start:  AIC=-343.04
## sl ~ sw + pl + pw

## 
## Call:
## lm(formula = sl ~ sw + pl + pw, data = iris)
## 
## Coefficients:
## (Intercept)           sw           pl           pw  
##      1.8560       0.6508       0.7091      -0.5565

step(m2,direction = "backward")

## Start:  AIC=-343.04
## sl ~ sw + pl + pw
## 
##        Df Sum of Sq    RSS     AIC
## <none>              14.445 -343.04
## - pw    1    1.8834 16.329 -326.66
## - sw    1    9.4353 23.881 -269.63
## - pl    1   15.4657 29.911 -235.86

## 
## Call:
## lm(formula = sl ~ sw + pl + pw, data = iris)
## 
## Coefficients:
## (Intercept)           sw           pl           pw  
##      1.8560       0.6508       0.7091      -0.5565