R语言从基础入门到提高（三）Vectors（向量）

第1程序：

Vector selection: the good times (2)

How about analyzing your midweek results?

To select multiple（多种） elements from a vector, you can add square brackets at the end of it. You can indicate（表明） between the brackets what elements should be selected.

For example: suppose you want to select the first and the fifth day of the week: use the vector c(1, 5) between the square brackets. For example, the code below（下面） selects the first and fifth element of poker_vector:

poker_vector[c(1, 5)]

选择啦第1，5元素

要求：

Assign the poker results of Tuesday, Wednesday and Thursday to the variable poker_midweek.

源码：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Define a new variable based on a selectionpoker_midweek <- poker_vector[c(2,3,4)]console：> # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Define a new variable based on a selection> poker_midweek <- poker_vector[c(2,3,4)]

第2程序：

Vector selection: the good times (3)

100xp

Selecting multiple elements of poker_vector with c(2, 3, 4) is not very convenient（方便）. Many statisticians are lazy people by nature（天性）, so they created an easier way to do this: c(2, 3, 4) can be abbreviated （简写）to2:4, which generates（引起） a vector with all natural numbers from 2 up to 4.

So, another way to find the mid-week results is poker_vector[2:4].

Notice how the vector 2:4 is placed between the square brackets to select element 2 up to 4.（这种写法是递增）

要求：

Assign to roulette_selection_vector the roulette（轮盘赌） results from Tuesday up to Friday; make use of : if it makes things easier for you.

源程序：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Define a new variable based on a selectionroulette_selection_vector <- roulette_vector[2:5]console： # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Define a new variable based on a selection> roulette_selection_vector <- roulette_vector[2:5]

第3程序

Vector selection: the good times (4)

100xp

Another way to tackle（处理） the previous exercise is by using the names of the vector elements (Monday, Tuesday, ...) instead of their numeric positions. For example,

poker_vector["Monday"]

will select the first element of poker_vector since "Monday" is the name of that first element.

Just like you did in the previous exercise with numerics, you can also use the element names to select multiple elements, for example:

poker_vector[c("Monday","Tuesday")]

直接使用变量名进行调用，选中。

要求：

• Select the first three（前3个） elements in poker_vector by using their names: "Monday", "Tuesday" and "Wednesday". Assign the result of the selection to poker_start.
• Calculate（计算） the average of the values in poker_start with the mean() function. Simply print out the result so you can inspect（检查） it.

源程序：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Select poker results for Monday, Tuesday and Wednesdaypoker_start <- poker_vector[c("Monday","Tuesday","Wednesday")]# Calculate the average of the elements in poker_start 直接计算平均数使用自带函数mean()mean(poker_start) #mark#重点理解console：> # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Select poker results for Monday, Tuesday and Wednesday> poker_start <- poker_vector[c("Monday","Tuesday","Wednesday")]>   > # Calculate the average of the elements in poker_start> mean(poker_start)[1] 36.66667

第4程序

Selection by comparison - Step 1

100xp

By making use of comparison（比较） operators（操作符）, we can approach（靠近） the previous question in a more proactive（先进） way.

The (logical) comparison operators known to R are:

• < for less than  不到； 少于
• > for greater than 大于
• <= for less than or equal to 小于等于
• >= for greater than or equal to 大于等于
• == for equal to each other 等于
• != not equal to each other 不等于

As seen in the previous chapter, stating 6 > 5 returns TRUE. The nice thing about R is that you can use these comparison operators also on vectors. For example:

> c(4, 5, 6) > 5[1] FALSE FALSE TRUE

我的理解是 第一个不是 大于号，而是R的输入提示

This command tests for every element of the vector if the condition stated by the comparison operator is TRUE or FALSE.

要求：

• Check which elements in poker_vector are positive（正数） (i.e. > 0) and assign this to selection_vector.
• Print out selection_vector so you can inspect（验证） it. The printout tells you whether you won (TRUE) or lost (FALSE) any money for each day.

源代码：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Which days did you make money on poker?selection_vector <- poker_vector[c(1,2,3,4,5)] > 0#mark#重点理解【刚开始时，我写的是selection_vector <- poker_vector[c(1,2,3,4,5) > 0 ]然后就出错啦，我没有选中向量元素就比较啦，只是选中啦向量中的下标（理解成下标吧）】# Print out selection_vectorselection_vectorconsole：> # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Which days did you make money on poker?> selection_vector <- poker_vector[c(1,2,3,4,5)]>0>   > # Print out selection_vector> selection_vector   Monday   Tuesday Wednesday  Thursday    Friday      TRUE     FALSE      TRUE     FALSE      TRUE

第5程序

Selection by comparison - Step 2

100xp

Working with comparisons will make your data analytical life easier. Instead of selecting a subset（子集） of days to investigate（研究） yourself (like before), you can simply ask R to return only those days where you realized a positive return for poker.

In the previous exercises you used selection_vector <- poker_vector > 0 to find the days on which you had a positive poker return. Now, you would like to know not only the days on which you won, but also how much you won on those days.

You can select the desired（渴望的） elements, by putting selection_vectorbetween the square brackets that follow poker_vector:

poker_vector[selection_vector]

R knows what to do when you pass a logical vector in square brackets: it will only select the elements that correspond to（对应是） TRUE in selection_vector.

要求：

Use selection_vector in square brackets to assign the amounts（总额） that you won on the profitable（获利的） days to the variable poker_winning_days.

源程序：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Which days did you make money on poker?selection_vector <- poker_vector > 0#选中获利的那些天，即poker_vector 表示所有元素，大于0的# Select from poker_vector these days#mark#重点理解poker_winning_days <- poker_vector[selection_vector]#将获利的那些天的获利额赋值给poker_winning_dayspoker_winning_days#打印console：> # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Which days did you make money on poker?> selection_vector <- poker_vector > 0> > # Select from poker_vector these days> poker_winning_days <- poker_vector[selection_vector]> poker_winning_days   Monday Wednesday    Friday       140        20       240

第6程序

Advanced selection

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Just like you did for poker, you also want to know those days where you realized a positive return for roulette.

要求：

• Create the variable selection_vector, this time to see if you made profit with roulette for different days.
• Assign the amounts that you made on the days that you ended positively for roulette to the variable roulette_winning_days. This vector thus contains the positive winnings of roulette_vector.

源程序：

# Poker and roulette winnings from Monday to Friday:poker_vector <- c(140, -50, 20, -120, 240)roulette_vector <- c(-24, -50, 100, -350, 10)days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")names(poker_vector) <- days_vectornames(roulette_vector) <- days_vector# Which days did you make money on roulette?selection_vector <- roulette_vector > 0# Select from roulette_vector these daysroulette_winning_days <- roulette_vector[selection_vector]console：> # Poker and roulette winnings from Monday to Friday:> poker_vector <- c(140, -50, 20, -120, 240)> roulette_vector <- c(-24, -50, 100, -350, 10)> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")> names(poker_vector) <- days_vector> names(roulette_vector) <- days_vector> > # Which days did you make money on roulette?> selection_vector <- roulette_vector > 0> > # Select from roulette_vector these days> roulette_winning_days <- roulette_vector[selection_vector]

这一章又完成啦。