使用dplyr过滤postgreSQL数据库中的多个值 [英] Filter multiple values in postgreSQL database with dplyr

问题描述

我想过滤一个postgres数据库，所以我可以把一个数据的子集进入R进行分析。我可以通过单个条件（选择一个featureid）成功进行过滤，但不能通过值向量进行过滤。例如，如果我设置与数据库的连接，那么

I want to filter a postgres database so I can bring a subset of the data into R for analysis. I can successfully filter by a single condition (pick a single featureid) but not by a vector of values. For example, if I set up the connection to the database as such

library(dplyr)
db <- src_postgres(dbname = 'conte_dev', host = '155.0.0.x', port = '1234', user = '...', password = '...')
tbl_daymet <- tbl(db, 'daymet')

那么如果我过滤到一个值，那么它的工作

then it works if I filter to a single value

  tbl_filtered <- tbl_daymet %>%
    dplyr::filter(featureid == 739554)

tbl_filtered

Source: postgres 9.3.5 [conte@127.0.0.1:5432/conte_dev]
From: daymet [12,410 x 9]
Filter: featureid == 739554 

   featureid       date     tmax     tmin  prcp    dayl  srad  vp   swe
1     739554 1980-01-18  -1.9375 -12.2500 0.000 32140.8 199.6 240 100.5
2     739554 1980-01-19   1.1250  -3.4375 0.000 32140.8 100.4 480  99.0
3     739554 1980-01-20   0.0000  -7.5000 0.000 32486.4 160.4 360  99.0
4     739554 1980-01-21  -6.5000 -15.7500 0.000 32486.4 193.6 180  99.0
5     739554 1980-01-22 -11.8125 -18.7500 0.000 32486.4 156.8 140  99.0
6     739554 1980-01-23  -6.4375 -16.5000 3.000 32832.0 157.2 160 102.5
7     739554 1980-01-24  -6.8750 -19.0000 3.125 32832.0 178.0 120 105.0
8     739554 1980-01-25 -15.0000 -23.0625 0.000 32918.4 184.4  80 105.0
9     739554 1980-01-26  -9.9375 -20.7500 0.000 33177.6 229.2 120 105.0
10    739554 1980-01-27  -7.0625 -15.9375 0.000 33177.6 202.4 165 105.0
..       ...        ...      ...      ...   ...     ...   ... ...   ...

但是，如果我尝试过滤到一组featureid

However if I try to filter to a group of values in featureid

catches <- c(739554, 739554)
tbl_derived_metrics <- tbl_daymet %>%
    dplyr::filter(featureid %in% catches)

我收到错误

postgresqlExecStatement（conn，statement，...）中的错误：RS-DBI
驱动程序:(无法检索t他的结果是：错误：或
附近的语法错误739554LINE 3：WHEREfeatureidIN 739554
^）另外：警告消息：在postgresqlQuickSQL（conn，statement，...）中：无法创建
executeSELECT count（*）FROM（SELECTfeatureid，date，tmax，
tmin，prcp，dayl，srad，vp ，sweFROMdaymetWHERE
featureidIN 739554）ASmaster

Error in postgresqlExecStatement(conn, statement, ...) : RS-DBI driver: (could not Retrieve the result : ERROR: syntax error at or near "739554" LINE 3: WHERE "featureid" IN 739554 ^ ) In addition: Warning message: In postgresqlQuickSQL(conn, statement, ...) : Could not create executeSELECT count(*) FROM (SELECT "featureid", "date", "tmax", "tmin", "prcp", "dayl", "srad", "vp", "swe" FROM "daymet" WHERE "featureid" IN 739554) AS "master"

我相信这样如果它是R中的数据帧，而不是postgres中的链接表，则可以工作。但是，我需要先进行过滤，因为该表包含几十行。有没有特别的命令我可以使用相关的postgres？

I believe this would work if it were a dataframe in R rather than a linked table in postgres. However, I need to do the filtering first since the table contains a few billion rows. Is there a special command I can use related to postgres? The current code doesn't work whether I use characters or integers.

推荐答案

使用％in％ 过滤器函数中的/ code>函数不起作用，如果它们只是一个值，而不是具有多个值的向量。

Using %in% in the filter function doesn't work if their is only a single value rather than a vector with multiple values.

它作为一个函数，对于具有1个或更多值的案例，它具有 ifelse 语句的功能。

It works as a function with an ifelse statement for cases with 1 or more values.

retreiveDaymet <- function(catchmentid, num.catch) {
  catches <- catchmentid[1:num.catch]
  if(num.catch == 1) {
    tbl_derived_metrics <- tbl_daymet %>%
      dplyr::filter(featureid == catches)
  } else {
    tbl_derived_metrics <- tbl_daymet %>%
    dplyr::filter(featureid %in% catches)
  }

  derived_metrics <- collect(tbl_derived_metrics)
  return(derived_metrics)
}

然后可以这样使用

catchment.numbers <- rep(c(1, 10, 50, 100, 200, 400, 800, 1000, 1500, 2000, 2500, 3000), each = 3)
daymet.times <- data.frame(matrix(NA, length(catchment.numbers), 4))
for(i in 1:length(catchment.numbers)) {
  time1 <- system.time(foo <- retreiveDaymet(catchmentid = catchmentid, num.catch = catchment.numbers[i]))
  daymet.times[i, ] <- c(catchment.numbers[i], time1[1:3])
  rm(foo)
  rm(time1)
  gc(verbose = FALSE)
}
names(daymet.times) <- c("num.catchments", names(system.time(1+1))[1:3])

这个例子有点傻，因为 foo 每次都被丢弃这只是用于计时的目的。在将来，此代码可以添加一个函数，以便每次使用 foo 执行某些操作，并将其附加到数据框或列表。

This example is a bit silly because foo is thrown away each time. This is just used for timing purposes. In the future this code could add a function to do something with foo each time and append it to a dataframe or list.

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