R- factor因子

因子(factor)

类别属性，只有有限数量的值。

The term factor refers to a statistical data type used to store categorical variables. The difference between a categorical variable and a continuous variable is that a categorical variable can belong to a limited number of categories.

# Sex vector sex_vector <- c("Male", "Female", "Female", "Male", "Male") # Convert sex_vector to a factor factor_sex_vector <- factor(sex_vector) # Print out factor_sex_vector factor_sex_vector

改变factor的值：

# Code to build factor_survey_vector survey_vector <- c("M", "F", "F", "M", "M") factor_survey_vector <- factor(survey_vector) # Specify the levels of factor_survey_vector levels(factor_survey_vector) <- c("Female", "Male")

注意：要按factor的顺序。

levels(factor_survey_vector)查看。

汇总信息查看：

# Build factor_survey_vector with clean levels survey_vector <- c("M", "F", "F", "M", "M") factor_survey_vector <- factor(survey_vector) levels(factor_survey_vector) <- c("Female", "Male") factor_survey_vector # Generate summary for survey_vector summary(survey_vector) # Generate summary for factor_survey_vector summary(factor_survey_vector)

结果

> summary(survey_vector)    Length     Class      Mode          5 character character > summary(factor_survey_vector) Female   Male       2      3

注：普通factor不可比较。

R returns NA when you try to compare values in a factor, since the idea doesn't make sense.

有序的factor，vector元素可比较。

# Create speed_vector speed_vector <- c("medium", "slow", "slow", "medium", "fast") # Convert speed_vector to ordered factor vector factor_speed_vector <- factor(speed_vector, ordered = TRUE, levels = c("slow", "medium", "fast"))

结果：

> factor_speed_vector [1] medium slow   slow   medium fast   Levels: slow < medium < fast > summary(factor_speed_vector)   slow medium   fast       2      2      1

比较元素：

> flg <- factor_speed_vector[1] > factor_speed_vector[2] > flg [1] TRUE