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Question

我写了以下代码

gem 'bootstrap-sass', '~> 3.3.6'
gem 'sass-rails', '~> 5.0'
bundle install

x看起来像：

a<-matrix(0,1,nrow = nrow(x))
for(i in 1:nrow(x)){
  for(j in 1:nrow(y)){
   if((y[j,3] > x[i,2]) & (y[j,2] == x[i,1])){
     a[i,]<- y[j,4]
     i<- i+1
   }
  }

和y看起来像

x1  x2
401 4
401 38
401 142...

我希望 y1 y2 y3 y4 1 401 10 22.152 2 401 40 167.986 3 401 70 393.198 4 401 100 923 5 401 120 923 6 401 140 686.712 7 401 160 865.774... 成为：

a

其中22.152 167.986 865.774... 为nrow(y) > nrow(x)。是否有可能提高效率？

Answer 1

使用data.table，我们加入on＆＃39; x1＆＃39;，＆＃39; y1＆＃39;来自＆＃39; x＆＃39;并且＆＃39; y＆＃39;，将i指定为y3 > x2，按＆＃39; x1＆＃39;分组和＆＃39; x2＆＃39;，获取第一行

library(data.table)
setDT(x)[y, on = .(x1 = y2), allow.cartesian = TRUE][y3 > x2, head(.SD, 1) , .(x1, x2)]
#    x1  x2 y1  y3      y4
#1: 401   4  1  10  22.152
#2: 401  38  2  40 167.986
#3: 401 142  7 160 865.774

数据

x <- read.table(text = "
  x1  x2
401 4
401 38
401 142", header = TRUE)

y <- read.table(text = "
y1 y2   y3    y4
1 401 10  22.152
2 401 40  167.986
3 401 70  393.198
4 401 100 923
5 401 120 923
6 401 140 686.712
7 401 160 865.774", header = TRUE)

Answer 2

我们可以使用dplyr

合并然后过滤

library(dplyr)

left_join(x, y, by = c("x1" = "y2")) %>% 
  filter(y3 > x2) %>% 
  arrange(y3) %>% 
  group_by(x1, x2) %>% 
  slice(1) 

# Source: local data frame [3 x 5]
# Groups: x1, x2 [3]
# 
#      x1    x2    y1    y3      y4
#   <int> <int> <int> <int>   <dbl>
# 1   401     4     1    10  22.152
# 2   401    38     2    40 167.986
# 3   401   142     7   160 865.774

数据

x <- read.table(text = "
  x1  x2
401 4
401 38
401 142", header = TRUE)

y <- read.table(text = "
y1 y2   y3    y4
1 401 10  22.152
2 401 40  167.986
3 401 70  393.198
4 401 100 923
5 401 120 923
6 401 140 686.712
7 401 160 865.774", header = TRUE)