Last updated: 2023-11-24

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Knit directory: bioinformatics_tips/

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Rmd ba521a7 Dave Tang 2023-11-24 Computer science

Computer science concerns the study of computation, automation, and information. Knowledge of some theory and principles in computer science will help you write better programs and pipelines.

Separation of concerns

Separation of concerns is a design principle for separating a computer program into distinct sections. Each section addresses a separate concern, such as pre-processing data or training a model, and leads to a modular program. This separation makes it easier to read and maintain code. While we can keep separating a task into finer details, it is useful in bioinformatics to keep code organised in specific tasks of a workflow/pipeline.

Time complexity

In theoretical computer science, the time complexity is the computational complexity that describes the amount of computer time it takes to run an algorithm. Time complexity is commonly estimated by counting the number of elementary operations performed by the algorithm, supposing that each elementary operation takes a fixed amount of time to perform.

Most commonly used classifications, sorted from the best (most efficient) to worst (least efficient):

Refactoring

From The Biostar Handbook:

Refactoring is an iterative process of improving code to reduce its redundancy and make it more generic and simpler. The reason we need refactoring is that typically a process becomes more well understood as we work and solve it. Periodically, we may need to revisit previous steps and rework them to match the later steps. Refactoring may feel wasteful, as often we modify what may seem to already be working just fine. But in any analysis, complexity can be a hindrance. Refactoring takes on complexity and attempts to simplify our work and will pay dividends in the future. Refactoring takes some practice and typically the returns are diminishing – that is, every code can be refactored, but after a few rounds of doing so the benefits are typically much smaller.

Storing states in bits

A bit array is an array data structure that compactly stores bits. It can be used to implement a simple set data structure. A bit array is effective at exploiting bit-level parallelism in hardware to perform operations quickly. A typical bit array stores kw bits, where w is the number of bits in the unit of storage, such as a byte or word, and k is some nonnegative integer. If w does not divide the number of bits to be stored, some space is wasted due to internal fragmentation.

This is a very compact way of storing data and is used to store properties of reads in BAM files.

samtools flags
About: Convert between textual and numeric flag representation
Usage: samtools flags FLAGS...

Each FLAGS argument is either an INT (in decimal/hexadecimal/octal) representing
a combination of the following numeric flag values, or a comma-separated string
NAME,...,NAME representing a combination of the following flag names:

   0x1     1  PAIRED         paired-end / multiple-segment sequencing technology
   0x2     2  PROPER_PAIR    each segment properly aligned according to aligner
   0x4     4  UNMAP          segment unmapped
   0x8     8  MUNMAP         next segment in the template unmapped
  0x10    16  REVERSE        SEQ is reverse complemented
  0x20    32  MREVERSE       SEQ of next segment in template is rev.complemented
  0x40    64  READ1          the first segment in the template
  0x80   128  READ2          the last segment in the template
 0x100   256  SECONDARY      secondary alignment
 0x200   512  QCFAIL         not passing quality controls or other filters
 0x400  1024  DUP            PCR or optical duplicate
 0x800  2048  SUPPLEMENTARY  supplementary alignment

sessionInfo()
R version 4.3.2 (2023-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 22.04.3 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.20.so;  LAPACK version 3.10.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] 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   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Etc/UTC
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] workflowr_1.7.1

loaded via a namespace (and not attached):
 [1] vctrs_0.6.4       httr_1.4.7        cli_3.6.1         knitr_1.44       
 [5] rlang_1.1.1       xfun_0.40         stringi_1.7.12    processx_3.8.2   
 [9] promises_1.2.1    jsonlite_1.8.7    glue_1.6.2        rprojroot_2.0.3  
[13] git2r_0.32.0      htmltools_0.5.6.1 httpuv_1.6.12     ps_1.7.5         
[17] sass_0.4.7        fansi_1.0.5       rmarkdown_2.25    jquerylib_0.1.4  
[21] tibble_3.2.1      evaluate_0.22     fastmap_1.1.1     yaml_2.3.7       
[25] lifecycle_1.0.3   whisker_0.4.1     stringr_1.5.0     compiler_4.3.2   
[29] fs_1.6.3          pkgconfig_2.0.3   Rcpp_1.0.11       rstudioapi_0.15.0
[33] later_1.3.1       digest_0.6.33     R6_2.5.1          utf8_1.2.4       
[37] pillar_1.9.0      callr_3.7.3       magrittr_2.0.3    bslib_0.5.1      
[41] tools_4.3.2       cachem_1.0.8      getPass_0.2-2