请看下面使用生成的示例
reprex
:
library(data.table)
DT <- data.table(id = letters[1:3], `counts(a>=0)` = 1:3)
DT[`counts(a>=0)` >= 2] # 1
#> id counts(a>=0)
#> 1: b 2
#> 2: c 3
DT[`counts(a>=0)` == 2] # 2
#> Error in `[.data.table`(DT, `counts(a>=0)` == 2): Column(s) [counts(a] not found in x
DT[id == "a"] # 3
#> id counts(a>=0)
#> 1: a 1
两行都用
#1
和
#3
工作,我想知道为什么要加入
`counts(a>=0)` == 2
(
#2
)没用。
会话信息:
> sessionInfo()
R version 3.4.4 (2018-03-15)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.4 LTS
Matrix products: default
BLAS: /usr/lib/atlas-base/atlas/libblas.so.3.0
LAPACK: /usr/lib/atlas-base/atlas/liblapack.so.3.0
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] reprex_0.1.2 data.table_1.11.2
loaded via a namespace (and not attached):
[1] Rcpp_0.12.16 rprojroot_1.3-2 digest_0.6.15 crayon_1.3.4 withr_2.1.2 assertthat_0.2.0 R6_2.2.2
[8] backports_1.1.2 magrittr_1.5 formatR_1.5 evaluate_0.10.1 stringi_1.1.6 debugme_1.1.0 rstudioapi_0.7
[15] callr_2.0.2 whisker_0.3-2 rmarkdown_1.9 devtools_1.13.5 tools_3.4.4 stringr_1.3.0 yaml_2.1.17
[22] compiler_3.4.4 htmltools_0.3.6 memoise_1.1.0 knitr_1.20
