Filter data.frame rows by a logical condition

Question

I want to filter rows from a data.frame based on a logical condition. Let's suppose that I have data frame like

   expr_value     cell_type
1    5.345618 bj fibroblast
2    5.195871 bj fibroblast
3    5.247274 bj fibroblast
4    5.929771          hesc
5    5.873096          hesc
6    5.665857          hesc
7    6.791656          hips
8    7.133673          hips
9    7.574058          hips
10   7.208041          hips
11   7.402100          hips
12   7.167792          hips
13   7.156971          hips
14   7.197543          hips
15   7.035404          hips
16   7.269474          hips
17   6.715059          hips
18   7.434339          hips
19   6.997586          hips
20   7.619770          hips
21   7.490749          hips

What I want to is to get a new data frame which looks the same but only has the data for one cell_type. E.g. subset / select rows which contains the cell type "hesc":

   expr_value     cell_type
1    5.929771          hesc
2    5.873096          hesc
3    5.665857          hesc

Or either cell type "bj fibroblast" or "hesc":

   expr_value     cell_type
1    5.345618 bj fibroblast
2    5.195871 bj fibroblast
3    5.247274 bj fibroblast
4    5.929771          hesc
5    5.873096          hesc
6    5.665857          hesc

Is there any easy way to do this?

I've tried:

expr[expr[2] == 'hesc']
# [1] "5.929771" "5.873096" "5.665857" "hesc"     "hesc"     "hesc"    

if the original data frame is called "expr", but it gives the results in wrong format as you can see.

Answer 1

To select rows according to one 'cell_type' (e.g. 'hesc'), use ==:

expr[expr$cell_type == "hesc", ]

To select rows according to two or more different 'cell_type', (e.g. either 'hesc' or 'bj fibroblast'), use %in%:

expr[expr$cell_type %in% c("hesc", "bj fibroblast"), ]