R勉強会 第五回 アウトプット用課題 解答例&解説

この記事はこちらの記事の解答例&解説です．作成途中です．

第1問

CV <- function(data){
  return(sd(data)/mean(data))
}

第2問

zero_one_scale <- function(vec){
  res <- (vec - min(vec))/(max(vec) - min(vec))
  return(res)
}

第3問

my_cumsum <- function(vec){
  res <- c()
  now <- 0
  for(x in vec){
    now <- now + x
    res <- append(res, now)
  }
  return(res)
}

第4問

test_of_no_correlation <- function(N, r){
  t <- (abs(r)*((N-2)**(1/2)))/((1-r**2)**(1/2))
  p <- 2*pt(t, N-2, lower.tail = FALSE)
  return(p)
}

第5問

extremum_detector <- function(data){
  n_points <- length(data)
  extremum_index <- c()
  for(i in 1:(n_points-4)){
    window <- data[i:(i+4)]
    zougen <- c()
    for(j in 2:5){
      zougen <- append(zougen, window[j] - window[j-1] >= 0)
    }
    if(sum(xor(zougen, c(TRUE, TRUE, FALSE, FALSE))) == 0 | sum(xor(zougen, c(T, T, F, F))) == 4){
      extremum_index <- append(extremum_index, i+2)
    }
  }
  return(extremum_index)
}

第6問

my_kmeans <- function(x, y, k){
  centroids <- list()
  for(c in 1:k){
    centroids <- append(centroids, list(c(sample(1:100,1), sample(1:100,1))))
  }
  now_cls <- rep(1, 50)
  while(1){
    next_cls <- c()
    for(i in 1:50){
      dist <- c()
      for(j in 1:k){
        dist <- append(dist, (centroids[[j]][1] - x[i])**2 + (centroids[[j]][2] - y[i])**2)
      }
      next_cls <- append(next_cls, which.min(dist))
    }
    if(sum(next_cls == now_cls) == 50){
      return(as.character(now_cls))
    }else{
      now_cls <- next_cls
      for(c in 1:k){
        centroids[[c]] <- c(mean(x[now_cls == c]), mean(y[now_cls == c]))
      }
    }
  }
}