今日Bash和R技巧总结

Posted 2021-05-02 普通学习者

(1) 将多个空格替换为1个空格
tr -s " " < file
(2) 去掉文本中最后4列
## 使用rev将最后4列变为前四列，再使用cut从第5行开始提取，假设分隔符为空格
cat myfile.txt | rev | cut -d ' ' -f5- | rev
(3) 在文本中查找某个字符串并返回该字符串所在的行
## 方法1
grep -n "string" myfile.txt
## 方法2
awk '/string/{print NR}' myfile.txt
## 方法3
cat -n myfile.txt | grep string
(4) 下载R包时指定镜像源
##先检查是否下载了pdftools包，并制定清华大学的镜像
    if ( ! 'pdftools' %in% rownames(installed.packages()))

    {install.packages("pdftools",repos='https://mirrors.tuna.tsinghua.edu.cn/CRAN/')}
(5) 在R中使用pdftools包提取pdf中的字符
## txt[1]表示pdf第一页的字符,txt[2]表示pdf第二页的字符
library(pdftools)
txt <- pdf_text("myfile.pdf")
参考：
(1) https://unix.stackexchange.com/questions/145978/replace-multiple-spaces-with-one-using-tr-only
(2) https://stackoverflow.com/questions/14418511/bash-method-to-remove-last-4-columns-from-csv-file
(3) https://stackoverflow.com/questions/30658703/how-to-print-the-line-number-where-a-string-appears-in-a-file
(4) https://stackoverflow.com/questions/19998927/sed-and-grep-get-the-line-number-for-a-match
(5) https://stackoverflow.com/questions/11488174/how-to-select-a-cran-mirror-in-r
(6) https://stackoverflow.com/questions/9341635/check-for-installed-packages-before-running-install-packages
(7) https://www.r-bloggers.com/introducing-pdftools-a-fast-and-portable-pdf-extractor/