RSQLite类型转换问题

时间:2012-10-10 16:58:35

标签: r sqlite

我正在尝试将SQLite数据库中的表写入R数据框,并且遇到了一个让我难过的问题。以下是我要导入的SQLite表中的三个第一个条目:

1|10|0|0|0|0|10|10|0|0|0|6|8|6|20000|30000|2012-02-29 21:27:07.239091|2012-02-29 21:28:24.815385|6|80.67.28.161|||||||||||||||||||||||||||||||33|13.4936||t|t|f||||||||||||||||||4|0|0|7|7|2
2|10|0|0|0|0|0|0|0|2|2|4|5|4|20000|30000|2012-02-29 22:00:30.618726|2012-02-29 22:04:09.629942|5|80.67.28.161|3|7||0|1|3|0|||4|3|4|5|5|5|5|4|5|4|4|0|0|0|0|0|9|9|9|9|9|||1|f|t|f|||||||||||||k|text|l|||-13|0|3|10||2
3|13|2|4|4|4|4|1|1|2|5|6|3|2|40000|10000|2012-03-01 09:07:52.310033|2012-03-01 09:21:13.097303|6|80.67.28.161|2|2||30|1|1|0|||4|2|1|6|8|3|5|6|6|7|6|||||||||||26|13.6336|4|f|t|f|t|f|f|f|f|||||||||some text||||10|1|1|3|2|3

我感兴趣的是第53到第60列,为了省去上面计算的麻烦,看起来像这样:

|t|t|f||||||
|f|t|f||||||
|f|t|f|t|f|f|f|f|

正如您在前两个条目中看到的那样,只有前三个列不是NULL,而对于第三个条目,所有八个列都分配了值。

以下是这些列的SQLite表信息

sqlite> PRAGMA table_info(observations);
0|id|INTEGER|1||1
** snip **
53|understanding1|boolean|0||0
54|understanding2|boolean|0||0
55|understanding3|boolean|0||0
56|understanding4|boolean|0||0
57|understanding5|boolean|0||0
58|understanding6|boolean|0||0
59|understanding7|boolean|0||0
60|understanding8|boolean|0||0
** snip **

现在,当我尝试将其读入R时,这些相同的列最终成为:

> library('RSQLite')
> con <- dbConnect("SQLite", dbname = 'db.sqlite3))
> obs <- dbReadTable(con,'observations')
> obs[1:3,names(obs) %in% paste0('understanding',1:8)]
  understanding1 understanding2 understanding3 understanding4 understanding5 understanding6 understanding7
1              t              t              f             NA             NA             NA             NA
2              f              t              f             NA             NA             NA             NA
3              f              t              f              0              0              0              0
  understanding8
1             NA
2             NA
3              0

如您所见,虽然前三列包含't''f'的值,但其他列为NA,其中SQLite表中的相应值为NULL并且< em> 0 它们不是 - 不管SQLite表中的相应值是t还是f。毋庸置疑,这不是我所期望的行为。我认为问题是这些列的类型错误:

> sapply(obs[1:3,names(obs) %in% paste0('understanding',1:8)], class)
understanding1 understanding2 understanding3 understanding4 understanding5 understanding6 understanding7 
   "character"    "character"    "character"      "numeric"      "numeric"      "numeric"      "numeric" 
understanding8 
     "numeric" 

当看到charactert作为第一个条目中相应列中的值但是{{1}时,RSQLite会将前三列设置为f类型因为在这些列中第一个条目恰好是NULL?

如果确实发生了这种情况,有什么方法可以解决这个问题,并将所有这些列投射到numeric(或者更好,character)?

1 个答案:

答案 0 :(得分:0)

以下是hacky,但它确实有效:

# first make a copy of the DB and work with it instead of changing
# data in the original
original_file <- "db.sqlite3"
copy_file <- "db_copy.sqlite3"
file.copy(original_file, copy_file) # duplicate the file
con <- dbConnect("SQLite", dbname = copy_file) # establish a connection to the copied DB

# put together a query to replace all NULLs by 'NA' and run it
columns <- c(paste0('understanding',1:15))
columns_query <- paste(paste0(columns,' = IfNull(',columns,",'NA')"),collapse=",")
query <- paste0("UPDATE observations SET ",columns_query)
dbSendQuery(con, query)

# Now that all columns have string values RSQLite will infer the 
# column type to be `character`
df <- dbReadTable(con,'observations') # read the table
file.remove(copy_file) # delete the copy

# replace all 'NA' strings with proper NAs
df[names(df) %in% paste0('understanding',1:15)][df[names(df) %in% paste0('understanding',1:15)] == 'NA'] <- NA
# convert 't' to boolean TRUE and 'f' to boolean FALSE
df[ ,names(df) %in% paste0('understanding',1:15)] <- sapply( df[ ,names(df) %in% paste0('understanding',1:15)], function(x) {x=="t"} )